Quick answer: “Molex MX1.25 wire-to-wire” is the trade shorthand for the Molex PicoBlade 1.25mm-pitch wire-to-wire connector system — the inline half of the PicoBlade family. It is a single-row, 2 to 15 circuit connector built from a 51021 receptacle housing mating with a 51047 plug housing, and its rating is higher than the wire-to-board system at the same pitch: 125V AC (RMS)/DC, with 2.0A at AWG #26, 1.5A at AWG #28, and 1.0A at AWG #30 and #32. It accepts AWG #26 to #32 with insulation from φ0.5mm to φ1.04mm, operates from −40°C to +105°C, and is rated for 30 mating cycles in the tin-plated version. The single most important thing to know is that the plug side and the receptacle side use different crimp terminals — 50058/50079 on the receptacle side and 50125/50133 on the plug side. The KONNRA KR1251 series is documented as the cross-reference equivalent.
At a glance
| Common trade name | Molex MX1.25 wire-to-wire · Molex 1.25mm W2W · “PicoBlade W2W” |
| Official Molex document | Product Specification 510211009-PS (wire-to-wire, tin plating) |
| Pitch | 1.25mm |
| Configuration | Single row, wire-to-wire (inline), friction lock, polarised |
| Housing pair | 51021 receptacle housing ↔ 51047 plug housing |
| Terminals — receptacle side | 50079 (AWG #26–28) · 50058 (AWG #28–32) |
| Terminals — plug side | 50125 (AWG #26–28) · 50133 (AWG #28–32) |
| Voltage rating | 125V AC (RMS)/DC |
| Rated current | 2.0A (AWG #26) · 1.5A (AWG #28) · 1.0A (AWG #30) · 1.0A (AWG #32) |
| Reference derating | 2.5A at 2 circuits (AWG #26) down to 1.0A at 10 circuits |
| Applicable wire | AWG #26 to #32 |
| Insulation O.D. | φ0.5mm to φ1.04mm |
| Contact resistance | 20mΩ max (5mΩ max crimped portion) |
| Insulation resistance | 100MΩ min |
| Dielectric strength | 250V AC (RMS), 1 minute |
| Operating temperature | −40°C to +105°C (including terminal temperature rise) |
| Durability | 30 cycles (tin plating) |
| Plating variant documented | Tin (a separate gold-plated specification also exists) |
| Plug housing material | Polyester, UL94V-0 |
| Standards | UL File E29179 |
| KONNRA equivalent | KR1251 |
What Is the PicoBlade Wire-to-Wire System?
The PicoBlade family covers two different connection types from one mutual contact system, and they are not the same product:
- Wire-to-board (W2B) — a cable half that mates onto a header soldered to a PCB. Molex’s specification for this is 510211000-PS, and KONNRA cross-references it as KR1250.
- Wire-to-wire (W2W) — two cable halves that mate to each other, with no board involved. Molex’s specification is 510211009-PS, and KONNRA cross-references it as KR1251.
Molex describes the PicoBlade as ideal for space-constrained wire-to-wire and wire-to-board applications, and the series has been a mainstream choice in compact consumer and industrial electronics for long enough that it functions as a de facto standard for small inline wiring.
Key characteristics:
- 1.25mm pitch, single row, inline wire-to-wire
- 51021 receptacle housing mates with a 51047 plug housing — two different housing series
- Friction lock with a mating lock — the 51047 plug housing has a lock to the mating part, and both halves are polarised so they mate in one orientation only
- Two-point contact design on each side
- Higher current than the wire-to-board system at the same pitch — 2.0A at AWG #26 against 1.0A
- 125V AC (RMS)/DC rating
- AWG #26 to #32, insulation φ0.5mm to φ1.04mm
- −40°C to +105°C operating range including terminal temperature rise
- 30-cycle mating durability in the tin-plated version
- UL File E29179
- Off-the-shelf pre-crimped leads and cable assemblies exist — Molex lists pre-crimped lead series 214922 and 214923 and a PicoBlade cable assembly series 15134
A short glossary, because this system has two of everything
- Receptacle housing — the half that carries the receptacle terminals. Molex’s series is 51021. In the wire-to-board system this same housing mates onto a board header; here it mates onto a plug housing.
- Plug housing — the mating half, carrying the plug terminals. Molex’s series is 51047. This housing does not exist in the wire-to-board system.
- Receptacle terminal — the crimp contact that goes into the 51021 housing. Series 50079 (AWG #26–28) and 50058 (AWG #28–32). These are the same terminals the wire-to-board system uses.
- Plug terminal — the crimp contact that goes into the 51047 housing. Series 50125 (AWG #26–28) and 50133 (AWG #28–32). These are different parts and they only fit the plug housing.
- Friction lock — retention by friction between the two housings, with no separate latch to release.
- Polarised — the housings are keyed so they can only be mated one way round.
- Panel mount — mounting a connector through an enclosure wall. The PicoBlade wire-to-wire housing is not a panel-mount part; Molex lists panel mounting as “No” for the 51047 series.
- Pre-crimped lead — a single wire with a terminal already crimped on, bought by the piece rather than assembled in-house.
- Dim T — Molex’s term for the minimum free length of wire between the connector and the first cable tie. On this series it is 50mm.
- Hot-mating — mating or unmating while current is flowing. Molex excludes it on this series.
Figure 1 — KONNRA KR1251 series: 1.25mm pitch PicoBlade wire-to-wire connector
➡️ View the KONNRA KR1251 MX1.25 Wire-to-Wire Connector
The Thing Nobody Tells You: The Two Sides Use Different Terminals
This is the single most important fact about the PicoBlade wire-to-wire system, and it is the one that costs the most when it is missed: the receptacle side and the plug side use different crimp terminals. They are different part number families, they are not interchangeable, and one complete inline harness needs both.
| Side | Wire range | Terminal series | Goes into |
|---|---|---|---|
| Receptacle | AWG #26–28 | 50079 | 51021 receptacle housing |
| Receptacle | AWG #28–32 | 50058 | 51021 receptacle housing |
| Plug | AWG #26–28 | 50125 | 51047 plug housing |
| Plug | AWG #28–32 | 50133 | 51047 plug housing |
The receptacle terminals are the same ones the wire-to-board system uses. The plug terminals are unique to the inline system and exist for no other purpose. So “I need PicoBlade 1.25mm terminals” is an incomplete specification, and ordering it that way has roughly a one-in-two chance of arriving with a reel you cannot crimp.
How to specify it correctly in two steps. First pick the pair that matches your wire gauge, then order both the receptacle and the plug version of that pair:
| Your wire | Receptacle terminal | Plug terminal |
|---|---|---|
| AWG #26–28 | 50079 series | 50125 series |
| AWG #28–32 | 50058 series | 50133 series |
AWG #28 is the overlap, and it is where harnesses go wrong. Both the 50079 and the 50058 are specified for AWG #28, and the same is true on the plug side — both the 50125 and the 50133 cover it. So at AWG #28 the conductor gauge does not tell you which pair to order. Choose by what the rest of your harness uses: if any circuit runs at AWG #26 or #27 you are in the heavier family, and if any circuit runs at AWG #29 or finer you are in the lighter one.
Insulation diameter is a single window across all four terminals on this system — φ0.5mm to φ1.04mm. That is simpler than the wire-to-board side, where the two terminal families had different insulation maxima (φ1.0mm and φ1.04mm).
Wire-to-Wire vs Wire-to-Board at the Same Pitch
The two halves of the PicoBlade family share a pitch, a contact system and a housing standard — and they do not share a current rating. Molex publishes separate specifications for each, and the figures differ.
| Parameter | Wire-to-Board (510211000-PS) | Wire-to-Wire (510211009-PS) |
|---|---|---|
| Voltage rating | 125V AC (RMS)/DC | 125V AC (RMS)/DC |
| Rated current, AWG #26 | 1.0A | 2.0A |
| Rated current, AWG #28 | 1.0A | 1.5A |
| Rated current, AWG #30 | 1.0A | 1.0A |
| Rated current, AWG #32 | 0.8A | 1.0A |
| Insulation O.D. | φ1.0mm / φ1.04mm max, by terminal | φ0.5mm to φ1.04mm |
| Derating table columns | 2 / 8 / 15 circuits | 2 / 6 / 10 circuits |
| Durability | 30 cycles (gold plating) | 30 cycles (tin plating) |
| Documented plating variant | Gold flash · 0.38µm gold · tin | Tin (a gold specification also exists separately) |
| KONNRA equivalent | KR1250 | KR1251 |
Three things follow from this table, and they matter more than the individual numbers:
- The inline system is rated higher at the heavy end — twice as high at AWG #26. 2.0A against 1.0A. If your inline connection runs AWG #26, the wire-to-wire PicoBlade is a materially more capable connector than its board-mounted sibling, even though they are the same family at the same pitch.
- But the two systems are identical at AWG #30, and the wire-to-board side is lower at AWG #32. So there is no single “PicoBlade current rating” — the answer changes with both the gauge and which half of the family you are using.
- Your harness takes the lowest rating in the chain. If a run goes from a board header, through a cable, to an inline joint and on to another board, the wire-to-board legs are the bottleneck at 1.0A — and a 2.0A inline joint in the middle of that run buys you nothing. Work out the limit from the weakest component, not the strongest.
The Current Rating Is Four Numbers, Not One
Molex publishes the wired-to-wire rated current per gauge, and then a separate reference derating table by circuit count.
Level 1 — rated current (MAX) by wire size. All four gauges share an insulation window of φ0.5mm to φ1.04mm.
| Wire size | Rated current (MAX.) |
|---|---|
| AWG #26 | 2.0A |
| AWG #28 | 1.5A |
| AWG #30 | 1.0A |
| AWG #32 | 1.0A |
Level 2 — reference derating by gauge and circuit count.
| AWG | 2 circuits | 6 circuits | 10 circuits |
|---|---|---|---|
| 26 | 2.5A | 2.0A | 2.0A |
| 28 | 2.0A | 1.5A | 1.5A |
| 30 | 1.5A | 1.0A | 1.0A |
| 32 | 1.3A | 1.0A | 1.0A |
Molex’s conditions for that table, stated in the specification: values are for reference only, deratings are based on not exceeding a 30°C temperature rise, temperature rise is measured in the barrel area of the crimp terminal, the data is for all circuits powered, and PCB trace design can greatly affect temperature rise results.
A caution about the derating columns. The wire-to-wire table uses 2, 6 and 10 circuits, while the wire-to-board table used 2, 8 and 15. The two tables are not interchangeable — do not carry a wire-to-board derating figure across to an inline design, or the reverse.
And the sum rule applies here too: Molex states that the sum of the current used on several circuits must not exceed the maximum allowable current, in addition to the per-circuit figure.
What this means when you cross-reference. KONNRA documents the KR1251 at a flat 1A. Against Molex’s wire-to-wire ratings that figure equals the AWG #30 and #32 rating, understates AWG #28 by a third, and understates AWG #26 by half. The critical gauge is AWG #26, where Molex rates 2.0A and the published KONNRA figure is 1A — so a 2-amp inline design risks being read as over-specification when in fact it sits inside the original part’s rating. State your gauge and current on the enquiry and have the figure confirmed for your design.
Molex PicoBlade Wire-to-Wire = KONNRA KR1251: Part Number Cross-Reference
| Molex PicoBlade W2W component | Molex part number | KONNRA equivalent |
|---|---|---|
| Receptacle housing | 51021 series (51021**00) |
KR1251 Housing |
| Plug housing | 51047 series (51047**00) |
KR1251 Housing (confirm which half) |
| Receptacle terminal, AWG #26–28 | 50079 series (500798**00) |
KR1251 Terminal |
| Receptacle terminal, AWG #28–32 | 50058 series (500588**00) |
KR1251 Terminal |
| Plug terminal, AWG #26–28 | 50125 series (501258**00) |
KR1251 Terminal |
| Plug terminal, AWG #28–32 | 50133 series (501338**00) |
KR1251 Terminal |
| Pre-crimped lead | 214922, 214923 | Built to order |
| Cable assembly | 15134 series | Built to order |
KONNRA documents two orderable components for this series, each with its own page:
| Component | KONNRA page |
|---|---|
| Housing | KR1251 Housing |
| Terminal | KR1251 Terminal |
Note the asymmetry, because it is the thing to resolve on the enquiry. Molex’s wire-to-wire system is built from two housing series and four terminal part numbers. KONNRA documents one housing and one terminal for KR1251. A wire-to-wire design needs to know which half of the pair it is buying — the 51021 receptacle side, the 51047 plug side, or both. Ask, and state whether you need the receptacle, the plug, or a matched set.
Figure 2 — KR1251 male (plug) housing
Figure 3 — KR1251 female (receptacle) housing
Figure 4 — KR1251 crimp terminal
The two housings are not made of the same material
Molex lists the 51047 plug housing as polyester, gender plug, with a lock to the mating part and polarisation, not glow-wire capable, and panel mount: no. The 51021 receptacle housing uses a polyamide material — Molex notes that its water absorption can change the insertion and withdrawal force and soften the click feel of the lock when mating.
That difference is worth knowing before you plan a service procedure. Molex’s own note on the receptacle housing: because it is polyamide, its water absorption status can change the insertion force, withdrawal force, or the feeling of insertion, and excessive absorption can interfere with insertion slightly or weaken the click feeling of the lock when mating — while not damaging the product’s function.
KONNRA documents a combined material list of PA66 / PBT / UL94 / Phosphor Bronze for the series, without separating the two halves. If your process or your customer’s specification names a material for a specific half, confirm which half it applies to.
Specification Differences to Verify Before You Cross-Reference
Ten points deserve attention before you sign off a wire-to-wire cross-reference.
- The current rating is four numbers on the Molex side and one on the KONNRA side. Molex rates the wire-to-wire system at 2.0A (AWG #26), 1.5A (AWG #28), 1.0A (AWG #30) and 1.0A (AWG #32). KONNRA documents a flat 1A, which matches the two finer gauges and understates the two heavier ones.
- The applicable wire range does not reach AWG #26 in the KONNRA documentation. Molex’s wire-to-wire system covers AWG #26 to #32. KONNRA’s stated KR1251 wire range is AWG #28 to #32 — the same gap as on the KR1250 side. AWG #26 is the gauge where this system’s advantage is concentrated (2.0A against the wire-to-board system’s 1.0A), so if your inline joint uses #26, say so.
- The insulation window is one-sided on the KONNRA side. Molex specifies φ0.5mm to φ1.04mm for this system — a two-sided window. KONNRA documents 1.0mm maximum with no minimum. A wire with insulation below 0.5mm is outside Molex’s specification and the KONNRA documentation gives no lower bound at all.
- Mating durability is published by Molex and not by KONNRA. Molex specifies 30 cycles for the tin-plated version. KONNRA publishes no cycle count for the KR1251 — and 30 is a low figure for an inline joint that a technician may separate to route a cable.
- Plating. Molex’s wire-to-wire document reviewed here is the tin-plated specification, and Molex publishes a separate gold-plated specification for the same system. KONNRA documents Tin over Nickel. So the finishes line up on the tin route — but if your design assumed gold, confirm which specification applies. On this series KONNRA’s own text is self-consistent (both its specification table and its advantages text say tin), unlike some other pages in the range.
- The housing and terminal count is the biggest structural gap. Molex’s wire-to-wire system is built from two housing series (51021 receptacle, 51047 plug) and four terminal part numbers (50079, 50058, 50125, 50133). KONNRA documents one housing and one terminal. Confirm which half of the pair you are ordering, and confirm the plug-side terminal separately from the receptacle-side terminal.
- Housing material is different on the two halves. Molex lists the 51047 plug housing as polyester, and the 51021 receptacle housing as polyamide — with a stated sensitivity to water absorption that can change the insertion and withdrawal force and soften the click feel of the lock. KONNRA documents a combined PA66 / PBT / UL94 list for the series without splitting the halves.
- Circuit range. Molex’s wire-to-wire rated-current and derating tables, and its insertion/withdrawal force table, run to 10 circuits; the wire-to-board tables run to 15. KONNRA documents KR1251 as 2 to 16 positions. Confirm the count you intend to order, and note that the wire-to-wire system has the narrower documented range of the two.
- Dielectric withstanding voltage matches — 250V AC (RMS) for 1 minute on both sides. This is one of the parameters that lines up, and it is worth stating because it does not on every part in this range. The rated voltage also matches at 125V.
- Standards. Molex lists UL File E29179. KONNRA’s product documentation states RoHS compliance, with UL certification asserted at brand level. If your qualification requires UL recognised status specifically for this part, ask for the file reference.
Design Cautions Worth Carrying Into Your Review
Molex publishes an unusually detailed set of usage constraints for this system — nineteen numbered notes in the wire-to-wire specification. They are not marketing; they are the failure modes the product is known to have, and they are the most useful content in the document. KONNRA does not publish an equivalent list.
On electrical and mechanical limits:
- Do not mate or unmate under load. Molex states the product is not designed for mating and unmating under an active electrical circuit, and that doing so may cause a spark and product damage. An inline joint is exactly the kind a technician is tempted to open live — write the procedure so that they do not.
- Respect the per-circuit rating, and the sum. The sum of the current across several circuits must not exceed the maximum allowable current, on top of the per-circuit figure.
- Tie the cable at least 50mm from the connector edge, with the tying force applied evenly across all wires. Molex defines that distance as a “free” length of wire — a length not subject to bias from a tie, a twist, or any bending that moves the wires out of their natural position. The wires must be dressed so that the terminals float freely in the pocket.
- No continuous pulling or stress force when mated. It can damage the contact area or the crimping.
- Do not hang loads on the connector — for example carrying the board by the harness while the connectors are engaged.
- After mating, do not let the boards apply pressure to the connector in the pitch direction, the span direction, or rotationally. Molex warns this can crack the solder or damage the connector.
On assembly and handling:
- Withdraw slowly, axially and straightly. Hold the wires together lightly and pull straight; angled or rough withdrawal can damage the connector.
- Mate along the mating axis. If diagonal mating is unavoidable, touch the external faces at under 10° and push from there.
- Use a new housing after extracting a terminal. Extracting a crimp terminal with a jig can deform the housing lance and reduce the terminal retention force enormously after re-insertion.
- Do not deform the lock part or the lance of the plug housing, or the terminals, on purpose — Molex lists this as a direct route to product failure.
- Protect the connector from external force and shock during harness assembly, packaging and transport. Molex warns this can deform the connector and degrade performance.
- Keep clearance between the connector and the chassis so no pressure is applied.
- Do not wash the connectors. Molex states this may damage the product’s function.
- Fix wires and PCB to the chassis to avoid sympathetic vibration. Sustained relative movement wears the contact area and causes contact defects.
- The applicable wire is, in principle, tin-plated copper stranded wire. Molex asks to be consulted and the wire evaluated in advance for anything else.
On appearance and expectations — these are not defects:
- Black spots, bubbles or a different shade in the plastic parts do not affect performance. Molex states this explicitly, including discolouration from ageing.
- The tin plating on the tail and nail can produce friction marks that transfer to neighbouring surfaces. Cosmetic only.
- Minor scratches on the housing surface and plating are possible. No performance impact.
- Ultraviolet exposure can discolour the plastic. No performance impact.
Components and Configuration Options
The KR1251 is documented as a two-part system, and the parts you need depend on which half of the pair you are building.
Housing
Two halves mate to make one inline joint, and they come from different Molex series — 51021 on the receptacle side, 51047 on the plug side. The plug housing carries the lock to the mating part and is polarised, so the pair mates in one orientation only. Molex lists the plug housing as not a panel-mount part.
Figure 5 — KR1251 1.25mm pitch male (plug) housing detail
Figure 6 — KR1251 1.25mm pitch female (receptacle) housing detail
Terminal
Four Molex part numbers across two sides and two wire ranges. See the terminal selection table above — both the side and the wire range have to be specified.
Series documentation
- KR1251 series engineering drawing (PDF)
- KR1251 product specification (PDF)
- KR1251 package specification (PDF)
➡️ Request drawings for the housing half and wire gauge you need
What the PicoBlade Wire-to-Wire System Is Used For
Molex positions the PicoBlade as ideal for space-constrained wire-to-wire and wire-to-board applications, and the inline system appears wherever two cable runs have to join with a releasable connection.
| Application | Why the inline PicoBlade fits |
|---|---|
| Joining two harnesses inside a compact device | 1.25mm pitch keeps the inline joint small enough to route through the same channels as the cable |
| Extending a run between two boards | No board header needed at the joint, so nothing has to be soldered at the intermediate point |
| Signal and low-power inline connections subject to shock or vibration | The two-point contact design and the friction lock with a mating lock exist for exactly this |
| Serviceable cable joints | A releasable inline connection lets a sub-assembly be swapped without cutting and re-crimping wires |
| Mixed runs where one end is a board header | The receptacle housing is shared between the wire-to-board and wire-to-wire systems, so the same contact system can appear at both ends of a run — but check the current rating, because the two halves do not share it |
| Above 125V-rated circuits | The 125V rating is more than twice JST’s GH series at the same 1.25mm pitch, which matters if your circuit runs above 50V |
| Compact consumer and handheld electronics | Molex’s long-standing mainstream position in this space, with off-the-shelf pre-crimped leads and cable assemblies available in the family |
| Automotive, medical and industrial process control | KONNRA positions the 1250/1251 range toward these sectors; confirm the automotive-grade variant and its LV214 / US CAR-2 certification if your programme requires it |
What it is not for. At a rated 2.0A maximum (AWG #26) it is a signal and low-power inline connector, not a power joint. It is not a panel-mount connector, so it cannot be used as a bulkhead feed-through without a separate mounting arrangement. And it is explicitly not for hot-mating — do not design a service procedure that opens this joint under load.
The 1.25mm Class: Where the Inline PicoBlade Sits
1.25mm is the most crowded pitch in the connector industry. Three manufacturers, at least six systems, and no two of them mate.
| Connector system | Type | Pitch | Current | Voltage | Wire | KONNRA equivalent |
|---|---|---|---|---|---|---|
| Molex PicoBlade wire-to-wire | W2W | 1.25mm | 2.0A (#26) · 1.5A (#28) · 1.0A (#30–32) | 125V | AWG #26–32 | KR1251 |
| Molex PicoBlade wire-to-board | W2B | 1.25mm | 1.0A (#26–30) · 0.8A (#32) | 125V | AWG #26–32 | KR1250 |
| Molex PanelMate | W2B | 1.25mm | 1A | 125V | — | KR1253 |
| Hirose DF13 | W2B | 1.25mm | 1A | 150V | — | KR1256 |
| Hirose DF14 | W2B | 1.25mm | 1A | 150V | — | KR1255 |
| JST GH | W2B | 1.25mm | 1A | 50V AC/DC | AWG #30–26 | KR1259 |
| Molex Pico-EZmate | W2B | 1.20mm | 1.5A | 50V | AWG 28–30 | KR1200 |
| JST ACH | W2B | 1.2mm | 2A (1–3 ckt) · 1.5A (4–5 ckt) | 50V AC/DC | AWG #32–28 | KR1201 |
” — ” means the figure is not verified from that manufacturer’s own documentation for this guide. The PanelMate, DF13 and DF14 rows are taken from KONNRA’s published series data; their pitch and current figures are consistent with the manufacturers’ own documentation.
Three things this table settles:
- “1.25mm” identifies a pitch, not a connector, and not a connection type. Six different systems sit at or near 1.25mm here, from three manufacturers. KONNRA cross-references them as KR1250 (PicoBlade W2B), KR1251 (PicoBlade W2W), KR1253 (PanelMate), KR1255 (DF14), KR1256 (DF13) and KR1259 (JST GH).
- A wire-to-wire option at this pitch is unusual. Nearly every other system in this table is wire-to-board only. The PicoBlade is the one where an inline joint and a board joint share the same receptacle housing (51021) and the same receptacle terminals (50058 / 50079) — so a designer can use one contact system at both ends of a run without doubling the qualification work.
- The inline version is the more capable one. At 2.0A on AWG #26, the wire-to-wire PicoBlade is rated twice its own wire-to-board sibling and twice JST’s GH series at the same pitch. Do not assume that a wire-to-wire joint is the weaker link — on this family it is the stronger one, and the bottleneck is usually the board end of the run.
Cable Assembly Options
KONNRA builds assemblies on the KR1251 interface in the standard harness configurations:
| Cable type | Description | Typical use |
|---|---|---|
| Single-ended inline joint | KR1251 on one end, bare wire leads on the other | Adapting a stock cable to an inline mate |
| Double-ended inline | KR1251 on both ends, same orientation | A complete drop-in replacement cable |
| Reversed inline | KR1251 on both ends, reversed orientation | Routing through a fold or hinge |
| Board-to-inline | KR1250 (board half) on one end, KR1251 (inline half) on the other | A complete run from a board header to a serviceable inline joint |
| Adapter and transition cables | KR1251 on one end, another interface on the other — for example PicoBlade to JST GH 1.25mm, or PicoBlade to SH 1.00mm | Where the two ends of a run use different series |
Two assembly notes that come straight from Molex’s own specification.
First, tie the cable at least 50mm from the connector edge, applying the force evenly across all wires. Molex defines that dimension as a “free” length of wire, precisely so that the terminals can float freely in their pockets. On an inline joint, where both ends can be pulled, this matters twice.
Second, Molex publishes the Application Tooling Specification separately, per terminal part number — not inside the product specification. Because this system has four terminal part numbers, a harness house needs the correct ATS for each side. If you are quoting the crimp specification, there are four of them.
Connector lead time is typically 2–3 weeks; wiring harness lead time is typically 3–4 weeks. Key materials are prestocked, and complete connector set samples can be delivered within 45 days.
➡️ Explore KONNRA wiring harness capabilities
Sourcing the PicoBlade Wire-to-Wire: What Procurement Teams Ask
Engineering decides that a connector will work. Procurement decides whether the supply chain around it is safe.
“Can you be a second source without changing our design?” That is what a documented cross-reference is for. The KR1251 is specified against the Molex PicoBlade 1.25mm wire-to-wire system — 1.25mm pitch, 125V rating, two-point contact design, friction lock with a mating lock, and a UL E29179 lineage on the original. We confirm equivalence against your specific part number, because the side of the pair, the wire gauge, the plating and the housing half all change the answer.
“What are your lead times?” Connector production lead time is typically 2–3 weeks. Wiring harness lead time is typically 3–4 weeks. Key materials are prestocked.
“How long for samples?” Complete connector set samples can be delivered within 45 days. On an inline system, a matched set matters: ask for both halves so the lock engagement and the click feel can be checked as a pair rather than as two loose parts.
“What qualifications do you hold?” ISO9001, ISO14001, IATF16949, ISO45001:2018, ISO13485, IPC620, and UL product and operational safety certifications. Automotive-grade series additionally hold LV214 and US CAR-2.
“How do we know the parts match your documentation?” A CNAS-accredited laboratory with 45+ sets of precision testing instruments, with dimensional and electrical verification data available on request. 95% of production processes carry full-line intelligent visual CCD inspection; automotive series receive 100% CCD inspection.
“Are you a manufacturer or a trader?” A manufacturer. Dongguan Konnra Electronics Co., Ltd., founded 2004, with in-house mould design, injection moulding, stamping, assembly, and inspection — so the connector and the cable assembly come from one quality system.
“What volumes can you support?” KONNRA reported 2025 sales of RMB 310 million, with connectors at 60% and wiring harnesses at 40% of the product mix, across four production bases with automation coverage exceeding 95%.
“Who else buys from you?” KONNRA states that it serves global cooperative clients including BYD, Volkswagen, and DJI.
➡️ Request the vendor qualification pack — certificates, test capability summary, product drawings, and a sample plan in one enquiry.
How to Get a Cross-Reference Check on Your Inline PicoBlade Part Number
Most wire-to-wire enquiries stall on the same thing: the buyer is not sure what information the supplier needs, so the enquiry never gets sent. On this system, one extra piece of information matters more than everything else.
Send us:
- Which half of the pair you need — the 51021 receptacle side, the 51047 plug side, or a matched set. This is the question that most often makes the difference between a correct and an incorrect quote.
- The original part number, if you have it — a housing such as
51021**00or51047**00, a receptacle terminal such as500798**00or500588**00, or a plug terminal such as501258**00or501338**00 - Wire gauge, and specifically whether it is AWG #26. Molex covers #26 to #32; the published KR1251 range is #28 to #32, so #26 needs to be raised explicitly
- Insulation outside diameter — Molex specifies φ0.5mm to φ1.04mm; KONNRA documents a 1.0mm maximum with no minimum
- Circuit count — Molex’s wire-to-wire tables run to 10 circuits; KONNRA documents 2 to 16
- Plating finish required, including whether you assumed gold. The document reviewed here is the tin-plated specification.
- Whether you need the connector only or a finished harness, and if a harness, the length and the far-end termination
- Your load current, so the AWG #26 2.0A question and the derating position can be settled rather than assumed
- Application and annual volume, so configuration, tooling and packaging can be matched to your programme
- A drawing or photo, if the part number is unreadable or the design has been reverse-engineered
When you send a part number, we will confirm four things against Molex’s own documentation: the side of the pair, the terminal family that matches your wire gauge, the housing series for the half you need, and the plating thickness you require. Those four are where an inline PicoBlade cross-reference most often goes wrong.
What you get back: a mapped KONNRA part number with the relevant product and engineering drawings, a specification comparison against your original part, and a sample and quote plan.
Engineer’s Pre-Release Checklist
Run this before you release a drawing for an inline PicoBlade-family connector.
- Connection type confirmed. The wire-to-board half is KR1250; the wire-to-wire half is KR1251. They share a pitch and a contact system and do not share a current rating.
- Both sides of the pair specified. Receptacle side uses 50079 / 50058; plug side uses 50125 / 50133. Two different families — one harness needs both.
- Wire gauge matched to the terminal family on each side, and AWG #26 confirmed in writing if you use it. Molex documents #26 to #32; the published KR1251 range is #28 to #32.
- Current checked per gauge, not per family — 2.0A (#26) · 1.5A (#28) · 1.0A (#30 and #32). The published KONNRA figure of 1A equals only the two finer gauges.
- The weakest link in the harness identified. A wire-to-board leg at 1.0A sets the limit for the whole run regardless of an inline joint rated 2.0A.
- Derating position established from your own board and your own tests. Molex’s values are reference only, based on a 30°C rise with all circuits powered, measured in the crimp barrel, and affected by PCB trace design. Use the wire-to-wire derating table, not the wire-to-board one — the columns differ (2/6/10 against 2/8/15).
- Sum of current across circuits checked against the maximum allowable, not just the per-circuit figure.
- Insulation outside diameter inside φ0.5mm to φ1.04mm, and note the KONNRA documentation publishes only a 1.0mm maximum with no minimum.
- Mating durability considered — Molex specifies 30 cycles in the tin-plated version; KONNRA publishes no figure.
- Plating variant confirmed — the specification reviewed here is the tin-plated one. Confirm whether your design assumed gold.
- Housing material confirmed for the half you need — polyester on the 51047 plug side, polyamide on the 51021 receptacle side, with a stated water-absorption sensitivity that can change insertion force and soften the lock click.
- Cable tie placed at least 50mm from the connector edge on both sides, force applied evenly, so the terminals float freely in their pockets. This is the retention answer for a friction-lock inline joint.
- Retention sized against reality. Withdrawal force is 2.8N minimum at 2 circuits, falling to 1.8N by the 30th cycle. The friction lock is not a cable retention device.
- Service procedure checked for hot-mating. Molex states this product is not designed for mating or unmating under an active circuit.
- Terminal extraction procedure written. Molex advises fitting a new housing after extracting a terminal, because the lance deforms and retention drops sharply.
- Mating axis alignment in the build instruction — straight, or under 10° if diagonal mating is unavoidable.
- Wire construction confirmed as tin-plated copper stranded, or raised for evaluation if it is not.
- Panel-mount requirement checked. The PicoBlade wire-to-wire housing is not a panel-mount part; a bulkhead feed-through needs a separate arrangement.
- Board pressure checked after mating — Molex warns against pressure in the pitch direction, the span direction or rotationally, which can crack solder joints.
➡️ Send us your drawing. We will review it against the KR1251 specification and come back with any mismatch we find — before you commit tooling. Submit a drawing for review
Why Source MX1.25 Wire-to-Wire Connectors from KONNRA
Dongguan Konnra Electronics Co., Ltd. (brand: KONNRA) was founded in 2004 and is a National High-Tech Enterprise specialising in connector and wiring harness research, development, production, and sales.
Manufacturing depth. A vertically integrated process covering precision mould design and manufacturing, automation design, precision injection moulding, stamping, assembly, and CCD visual inspection. Automation coverage exceeds 95% across production lines.
Testing and validation. A CNAS-accredited laboratory with 45+ sets of precision testing instruments, and CAE analysis — contact nonlinear analysis, material nonlinear analysis, motion simulation, thermal field analysis, and high-frequency analysis — performed in Ansys 2022 R1. Verification data is available on request.
Inspection coverage. Full-line intelligent visual CCD inspection covers 95% of production processes, using Mitsubishi and Panasonic PLC control systems with FA25–35mm optical lenses and 5-megapixel cameras. Automotive connector series receive 100% CCD visual inspection.
Quality systems. ISO9001, ISO14001, IATF16949, ISO45001:2018, ISO13485, IPC620, and UL product and operational safety certifications, with automotive-grade series additionally certified to LV214 and US CAR-2.
Capacity and delivery. Production bases in Dongguan Wangniudun (30,000 m², 350+ employees), Dongguan Changan (10,000 m², 150+ employees), and Hunan Daoxian (2,600 m², 100+ employees), with regional offices in Beijing, Chongqing, Hunan, Shanghai, and Kunshan. Key materials are prestocked, and complete connector set samples can be delivered within 45 days. KONNRA reported 2025 sales of RMB 310 million, with connectors at 60% and wiring harnesses at 40% of the product mix, and has served global cooperative clients including BYD, Volkswagen, and DJI.
Custom and joint R&D. Where a standard part does not fit — the AWG #26 path, a specific plating, a matched receptacle-and-plug set, or a transition to another interface — KONNRA supports customer joint R&D customisation.
How to Identify Whether Your Connector Is a PicoBlade Wire-to-Wire
If you are holding a connector and a drawing you cannot match, work through these in order:
- Establish whether it is a cable-to-cable joint or a cable-to-board joint. If both sides are wires, you have the wire-to-wire system — KONNRA cross-references that as KR1251. If one side is a board header, it is the wire-to-board system — KR1250.
- Measure the pitch. 1.25mm points at Molex PicoBlade, Molex PanelMate, Hirose DF13/DF14 or JST GH. 1.20mm points at Molex Pico-EZmate or JST ACH. 1.00mm points at Molex Pico-Clasp or JST SH.
- Count the positions. Molex’s wire-to-wire rating and force tables run to 10 circuits; the wire-to-board tables run to 15.
- Look at the housings. The plug half should carry a lock to the mating part and be polarised. The pair mates in one orientation only.
- Look at the contact geometry. The two-point contact design is the PicoBlade signature; a single-point contact at this pitch indicates a different series.
- Check the plating colour. This specification is tin-plated; a distinctly gold contact area means a different PicoBlade specification applies.
- Read the part number if there is one. 51021 is the receptacle housing, 51047 is the plug housing, 50058 / 50079 are receptacle terminals, and 50125 / 50133 are plug terminals.
If you are still unsure, photograph both halves next to a ruler, with any part number markings visible, and send it to us. At this pitch, the measurement identifies the family; which half each part belongs to identifies the terminal you need.
Frequently Asked Questions
What is a Molex MX1.25 wire-to-wire connector?
It is the trade shorthand for the Molex PicoBlade 1.25mm-pitch wire-to-wire connector system — a single-row inline connector in 2 to 15 circuits, built from a 51021 receptacle housing mating with a 51047 plug housing, rated 125V AC (RMS)/DC with 2.0A at AWG #26, 1.5A at AWG #28 and 1.0A at AWG #30 and #32.
What is the difference between the wire-to-wire and wire-to-board PicoBlade?
The connection type and the current rating. Wire-to-wire joins two cable halves with no board involved; wire-to-board mates a cable onto a soldered header. Electrically, the wire-to-wire system is rated higher at the heavy end — 2.0A at AWG #26 against 1.0A for the wire-to-board system, and 1.0A against 0.8A at AWG #32 — while the two are identical at AWG #30. Molex publishes them as separate specifications, and KONNRA cross-references them as KR1251 and KR1250.
Which terminals does the PicoBlade wire-to-wire system use?
Four part numbers across two sides. The receptacle side uses the 50079 series for AWG #26–28 and the 50058 series for AWG #28–32. The plug side uses the 50125 series for AWG #26–28 and the 50133 series for AWG #28–32. The plug terminals are unique to the inline system and are not interchangeable with the receptacle terminals — one complete inline harness needs both families.
How do I pick the right terminal for my wire?
Match the wire gauge to the family on each side. For AWG #26–28 you need the 50079 (receptacle) and 50125 (plug); for AWG #28–32 you need the 50058 (receptacle) and 50133 (plug). AWG #28 is covered by both families, so at that gauge the conductor does not decide — choose by what the rest of the harness uses.
What is the current rating of the PicoBlade wire-to-wire connector?
2.0A at AWG #26, 1.5A at AWG #28, 1.0A at AWG #30 and 1.0A at AWG #32, at a maximum voltage of 125V AC (RMS)/DC. Molex also publishes a reference derating table by gauge and circuit count running up to 2.5A at 2 circuits with AWG #26 — but Molex marks those values as reference only, based on a 30°C temperature rise with all circuits powered, and states that PCB trace design greatly affects the result.
Why is the wire-to-wire rating higher than the wire-to-board rating at the same pitch?
Both systems share a 1.25mm pitch and a two-point contact design, but Molex publishes a separate product specification for each, with different rated currents. The practical consequence is that your harness takes the lowest rating in the chain — a wire-to-board leg at 1.0A limits a run even when the inline joint in the middle is rated 2.0A.
What is the voltage rating of the PicoBlade wire-to-wire connector?
125V AC (RMS)/DC — the same as the wire-to-board system, and more than twice the 50V rating of JST’s GH series at the same 1.25mm pitch.
What wire does the PicoBlade wire-to-wire connector use?
AWG #26 to #32, with an insulation outside diameter of φ0.5mm to φ1.04mm across all four terminals. Molex specifies that the applicable wire is, in principle, tin-plated copper stranded wire, and that other constructions should be evaluated first.
How many circuits does it come in?
Molex’s wire-to-wire rated-current and derating tables, and its insertion and withdrawal force table, run from 2 to 10 circuits — narrower than the wire-to-board tables, which run to 15. KONNRA documents the KR1251 as 2 to 16 positions.
What is the durability of the PicoBlade wire-to-wire connector?
30 mating cycles in the tin-plated version, per Molex. Molex’s own force table shows withdrawal force on a 2-circuit connector falling from 2.8N to 1.8N by the 30th cycle. KONNRA does not publish a cycle count for the KR1251.
Is the PicoBlade wire-to-wire connector panel mount?
No. Molex lists panel mounting as “No” for the 51047 plug housing. A bulkhead feed-through requires a separate mounting arrangement.
What are the two housings made of?
Molex lists the 51047 plug housing as polyester and the 51021 receptacle housing as polyamide. Molex notes that the receptacle housing’s water absorption can change the insertion and withdrawal force and weaken the click feeling of the lock when mating, without damaging the product’s function.
Can the connector be mated under load?
No. Molex states that this product is not designed for mating and unmating under an active electrical circuit, and that doing so may cause a spark and product defect. On an inline joint this matters more than on a board connector, because an inline joint is exactly the kind a technician is tempted to open live.
How far from the connector should I tie the cable?
Molex specifies a minimum of 50mm between the connector edge and the cable tie, with the tying force applied evenly across all wires. Molex defines that distance as a free length of wire, so that the terminals float freely in the pocket. On an inline joint you need a tie at each end.
Can I reuse the housing after extracting a terminal?
Molex advises against it. Extracting a crimp terminal with a jig can deform the housing lance, and Molex states this can “reduce the terminal retention force enormously” after re-insertion. The guidance is to fit a new housing when repairing crimp terminals.
What are the insertion and withdrawal forces?
Withdrawal force minimum ranges from 2.8N on a 2-circuit connector to 5.8N on a 10-circuit connector at first mating, falling to 1.8N and 4.8N respectively by the 30th cycle. Crimp pull-out force is 9.8N minimum at AWG #26 and #28, and 4.9N at AWG #30. Crimp terminal retention in the housing is 4.9N minimum.
What is the contact resistance and insulation resistance?
Contact resistance 20mΩ max and insulation resistance 100MΩ min; the crimped portion is specified separately at 5mΩ max. All of those figures are common to the wire-to-board system as well. Note that after vibration, shock, temperature cycling, heat, cold, humidity, salt spray and gas exposure, contact resistance is allowed to rise to 40mΩ max.
What tests does the wire-to-wire specification cover?
Vibration (1.5mm P-P, 10–55–10 Hz, 2 hours in each of three axes), mechanical shock (50G for 11ms, 18 shocks), temperature cycling (−55°C to +105°C, 5 cycles), heat resistance (85°C for 96 hours), cold resistance (−40°C for 96 hours), humidity (60°C at 90–95% RH for 96 hours), salt spray (5% NaCl for 48 hours at 35°C), SO₂ gas (50ppm for 24 hours at 40°C) and NH₃ gas. Contact resistance is allowed to reach 40mΩ max after each.
What standards does it hold?
Molex lists UL File Number E29179. KONNRA’s product documentation states RoHS compliance, with UL certification asserted at brand level.
How long does it take to get samples?
KONNRA can deliver complete connector set samples within 45 days. Connector production lead time is typically 2–3 weeks and wiring harness lead time typically 3–4 weeks.
Start Your Cross-Reference Check
KONNRA supplies the KR1251 series as individual components or as complete pre-crimped cable assemblies, and builds adapter and transition harnesses to order.
- Request a quote — KR1251 pricing, MOQ and configuration options for your circuit count and half of the pair
- Request a connected set — matched receptacle and plug halves so the lock engagement and click feel can be checked as a pair
- Request cross-reference verification — confirm KR1251-to-PicoBlade equivalence against your specific part number, including the terminal for your wire gauge
- Request AWG #26 confirmation — this gauge is inside Molex’s range and outside the published KR1251 range, and it is where this system’s 2.0A advantage sits
- Request drawings — series engineering drawing, product specification and package specification
- Request a vendor qualification pack — certificates, test capability summary and quality documentation
- Request adapter harnesses — PicoBlade to JST GH 1.25mm, PicoBlade to SH 1.00mm, or another interface on the far end
- Submit a drawing for review — we will flag any specification mismatch before you commit tooling
Contact KONNRA Electronics
- Phone: (86)-769-85449875
- Email: info@konnra.com
- Address: No.6 Nanchang South Road, Chijiao, Wangniudun, Dongguan, Guangdong, China
- Contact us
➡️ Explore the full 1.25mm pitch range · Wire-to-wire connector catalogue · Molex connector alternatives
Sources and method. Molex PicoBlade wire-to-wire figures are taken from Molex’s published Product Specification 510211009-PS (revision B, “PicoBlade 1.25 WTW Tin Plating Connector Smart Spec”): the 125V AC (RMS)/DC voltage rating; the rated current of 2.0A at AWG #26, 1.5A at AWG #28, 1.0A at AWG #30 and 1.0A at AWG #32 with an insulation diameter of φ0.5mm to φ1.04mm; the reference current derating table by gauge and circuit count with its stated conditions of a 30°C maximum temperature rise, measurement in the barrel area of the crimp terminal, all circuits powered, and the caveat that PCB trace design greatly affects the result; the −40°C to +105°C ambient temperature range including terminal temperature rise; the 20mΩ maximum contact resistance, the 5mΩ maximum crimped-portion contact resistance and the 40mΩ maximum after environmental exposure; the 100MΩ minimum insulation resistance; the 250V AC (RMS) one-minute dielectric strength test; the 30-cycle durability for tin plating; the insertion and withdrawal force table by circuit count from 2 to 10 circuits; the crimp pull-out, terminal insertion force and terminal retention force values; the vibration, mechanical shock, temperature cycling, heat, cold, humidity, salt spray, SO₂ and NH₃ gas tests with their conditions; the UL File Number E29179; the part numbers and drawing numbers for the 50079 and 50058 receptacle terminals, the 50125 and 50133 plug terminals, the 51021 receptacle housing and the 51047 plug housing; and the nineteen numbered usage notes. The 51047 plug housing’s polyester material, plug gender, lock to mating part, polarisation, glow-wire capability and non-panel-mount status, its mating with the 51021 receptacle housing, and the existence of the 214922 and 214923 pre-crimped lead series and the 15134 cable assembly series are taken from Molex’s published part data for the 51047 series. The wire-to-board comparison figures are from Molex’s separate Product Specification 510211000-PS. The comparison-table figures for Molex Pico-EZmate, JST ACH, JST GH and Hirose DF13/DF14 are taken from those manufacturers’ own published documentation where available, and from KONNRA’s published series data where noted. KONNRA KR1251 specifications, component pages and download links are taken from KONNRA’s published product and component documentation. Where the two sources disagree, or where a figure differs between two places on the same source, the difference is stated in this guide rather than smoothed over. Always confirm final dimensional and electrical requirements against the current manufacturer drawing for your specific part number.
