"Board-in" is the one connector term that people read as a mounting style when it is actually an architecture — and the difference decides whether your cross-reference is even the right part.

A board-in connection has no board header at all. There is no wafer, no pin block soldered to the PCB, no second solder joint. The crimp housing itself is the component mounted at the board, and the crimped wire terminals load into it from the wire side. Molex states the design intent directly: board-in connectors "meet the requirements of a cost-effective easy-to-assemble connection that does not need to be unmated on at least one end."

That single sentence is a test you can apply in ten seconds. If your design shows a board-mounted header that a wire-side housing plugs onto, you do not have a board-in design — and no amount of pitch matching will make the board-in cross-reference fit. You want the wire-to-board branch of the family instead.

I work on connector and harness programmes at KONNRA, which builds a documented cross-reference to this system (the KR1252). Here is what actually matters about the part, and the four documentation traps I would check before signing off a cross-reference.

What the Molex MX1.25 board-in system is

"MX1.25" is trade shorthand built from the 1.25mm pitch. On the board-in side of Molex's catalogue it maps to the 51022 Board-in Crimp Housing and its matching male crimp terminals. Molex's own product name field for these parts is simply "Board-in".

• Pitch: 1.25mm, single row, vertical (the wire exits perpendicular to the board)
• Housing: 51022 series, Polyester, colour Natural
• Terminals: 50061 series for AWG 28, 30, 32 · 50080 series for AWG 26, 28
• Terminal material: phosphor bronze, tin plated — minimum 0.889µm on the mating area and 0.914µm on the termination area
• Circuits: 2 to 15 by part number, 51022-0200 through 51022-1500
• Voltage: 125V maximum
• Current: 1.0A maximum per contact, and 0.8A at AWG 32
• Wire insulation diameter: 0.50mm to 1.00mm (50061)
• Operating temperature: −40° to +85°C (51022 housing)
• Wafer / board header: not applicable — that is the whole point of board-in
• KONNRA equivalent: KR1252
• Pre-crimped leads: if your board-in side stays original Molex, Molex lists 797581062 and 797581063 — ready-made leads that plug straight into the 51022 housing

Trap 1: "MX1.25" covers four different Molex systems

This is where cross-references go wrong before any specification is even compared. Molex runs at least four separate systems at 1.25mm pitch, they share nothing but the pitch, and the trade name is used loosely for all of them:

• Board-in — 51022 housing, 50061 / 50080 terminals → KONNRA KR1252
• PicoBlade wire-to-board — 51021 housing, 50079 / 50058 terminals, plug assemblies 53047 / 53048 → KONNRA KR1250 (wire-to-board) and KR1251 (wire-to-wire)
• CLIK-Mate wire-to-board — 502380 housing family → no equivalent documented against KR1252
• PanelMate wire-to-board — 51146 housing family → no equivalent documented against KR1252

A drawing that says "1.25mm Molex" and nothing else cannot be quoted from the pitch alone. Board-in, PicoBlade, CLIK-Mate and PanelMate all look like neighbours in a parts list. And there is a second divider beyond the architecture: board-in parts have no separate latch to release, because at least one end is not meant to be unmated. If repeated mating is a requirement of your design, you are looking at the wrong branch.

Trap 2: the cross-reference target itself may be obsolete

Worth checking before anything else on an existing design: Molex's part page for 50080-8000 lists the series as Obsolete, with the replacement instruction "Contact Molex", and points to 50080-8100 as the loose-packaging alternative. An older distributor snapshot of the same part, dated 2013, still shows the status as Active — so the two sources disagree.

If your drawing calls out 50080, the second-source exercise is not optional. And note the sizing: 50080 is the 26–28 AWG terminal; 50061 is the 28–32 AWG one.

Trap 3: KONNRA's own documentation disagrees with itself on two rows

This is normal for a cross-reference and easy to miss, because both documents are legitimate:

• Voltage rating. KONNRA's product page states 125V, its Overview paragraph says "voltage ratings up to 125V AC/DC", and both component pages state operating voltage 125V. But the series specification PDF, PS-KR1252-01 clause 4.0, states "Rated Voltage (Max.) 50V AC/DC". Molex publishes 125V maximum for the 50061 board-in terminal. So two of KONNRA's three published levels agree with Molex and the third does not — and the third is the document an engineer is most likely to attach to a drawing. If your application runs above 50V, or if the receiving-inspection document will be the specification PDF, resolve it in writing.
• Wire insulation diameter. The specification PDF and both component pages state 1.00mm maximum. The product page General Specification table states "Insulation O.D 1.25mm" — which is the pitch. That is the signature of a transcription error. Molex documents 0.50mm to 1.00mm for 50061. Three KONNRA sources say 1.00mm, one says 1.25mm.

Trap 4: the component page names the wrong half of the Molex terminal pair

KONNRA's housing page names the Molex 51022 series, which is correct — 51022 is the board-in housing. But its terminal page names the Molex 50080 series while documenting the terminal for AWG 28# to 32# — and in Molex's catalogue 28–32 AWG is the 50061 range; 50080 is the 26–28 AWG part.

So the component page points at the wrong half of the pair for its own published wire range. That is a documentation mismatch rather than an electrical one, but it is exactly the kind of thing that ends up copied onto a BOM. Resolve it in writing, at the same time as the 50080 obsolescence question — they are the same conversation.

Where the two sides genuinely agree — including one row that is right here

Worth stating, because on a cross-reference it is not a given: contact resistance 20mΩ max on both sides · insulation resistance 100MΩ min on both sides · pitch, single row and vertical mating direction · dielectric withstanding voltage 250V AC for 1 minute on both sides.

That last one deserves a note, because on some KONNRA series this row is filled in wrongly — with the rated voltage copied into the dielectric test row. Here it is not. KONNRA's specification states 250V AC for 1 minute between adjacent terminals or terminal and ground, with the requirement "no breakdown and flashover", and the rated voltage on its pages is 125V. 250V is a genuine dielectric test value, not a mis-copied rating. The only caveat is provenance: the 250V figure on the Molex side comes from the 1.25mm PicoBlade system specification, because Molex's board-in product specification (PS-51022-001) is referenced from its part pages but the PDF itself was not retrievable when this was written.

Where they differ materially

• Operating temperature — a 20°C difference, with no headroom above KONNRA's own claim. Molex documents −40° to +85°C for the 51022 housing. KONNRA documents −40°C to +105°C, and backs the upper figure with a heat-resistance test at 105±2°C for 96 hours. The KONNRA part is claimed over a wider window — but its own heat-ageing test runs at exactly 105°C, so treat the upper limit as a hard ceiling, not a conservative claim with margin behind it.
• Housing material. Molex specifies Polyester; KONNRA specifies Nylon66 (PA66) with a UL94V-0 rating, colour White against Molex's Natural. Different polymers with different moisture uptake, dimensional behaviour under thermal cycling and reflow tolerance — a process question, not a datasheet footnote, if the housing sees reflow or a wash. And note the comparison is not "rated versus unrated": Molex's 51022 datasheet does not state a flammability rating, so this is two different materials, one of which carries a published V-0 claim.
• Plating construction. Molex: tin at a stated minimum thickness on mating and termination. KONNRA: tin plated over nickel, thickness not documented. Tin-over-nickel is a different construction from tin directly on phosphor bronze, and not equivalent in porosity or long-term contact stability. Ask for both layer thicknesses in microns.
• Circuit count — 2 to 15 versus 2P to 16P. One position wider on the KONNRA side. Confirm the exact count before it reaches a drawing; a 16-position 1.25mm board-in housing is outside Molex's documented range.
• Durability — published by Molex, not by KONNRA. The 1.25mm system specification states 30 cycles for tin-plated parts. KONNRA publishes no cycle count. On a board-in part the question is narrower than on a mating pair, since the interface is not designed for repeated unmating — but if the housing will be re-loaded during assembly rework, ask for a figure.
• Standards. Molex references UL File E29179 (via the 1.25mm system specification); the KONNRA housing and terminal pages list UL file E482542. Different files — worth noting if your qualification names one.

What board-in changes about your design

This is the part that a bill-of-materials comparison will not tell you. Four consequences:

1. The crimp becomes the only compliant joint between the wire and the board. With no header and no second solder joint, there is nothing else in the path. That raises the importance of crimp quality from a harness detail to a board-level reliability item. KONNRA publishes unusually specific crimp acceptance criteria for exactly this reason: crimp width 0.85±0.1mm, conductor crimp height bands of 0.50–0.60mm at AWG 28, 0.45–0.55mm at 30 and 0.40–0.50mm at 32, insulation crimp height of 1.15 / 1.05 / 0.85mm maximum at 28 / 30 / 32 AWG, minimum crimp strength of 1.36 / 0.9 / 0.7 kgf at 28 / 30 / 32 AWG, and a strip length of 1.1 to 1.5mm. Those numbers belong in the purchase order rather than being left to a harness house's default — and Molex does not publish a directly comparable crimp sheet for the board-in terminal, so the two documents are not interchangeable.
2. Retention is specified, and it is small. KONNRA documents terminal insertion force at 0.5kgf (4.9N) maximum and terminal-to-housing retention at 0.7kgf (6.86N) minimum. Single-digit newtons, with no latch. The wire must not be loaded in tension, and the harness needs strain relief and a defined service loop — specify the cable tie or twist tie location on the drawing rather than leaving it to the line.
3. The 0.5kgf insertion force is a process limit, not just a spec. A terminal that needs more than that to seat is not a terminal that should be pushed harder — it is a terminal that is not entering correctly.
4. Insulation diameter is a real constraint at this pitch. 1.25mm pitch with a 1.00mm maximum jacket leaves very little room between adjacent wires. A heavier jacket that still passes the crimp barrel can make the wires bear on each other across the contact field. Measure the jacket, not the conductor — and check the daisy-chain case, because a 16-position housing with full-gauge wire is the tightest configuration in the family.

What it is not for. It is not a high-current connector — 1A per contact, and 0.8A at AWG 32 on the Molex terminal. It is not a repeatedly mated interface, because the architecture is designed so that at least one end stays put. And it is not a wire-to-board system: if you need a board header with a plug, you want the PicoBlade branch.

What to send for a cross-reference check

1. The original Molex part number, if you have it — a housing such as 51022-0200 or 51022-1500, or a terminal such as 50061-8000 or 50080-8000
2. Position count — Molex's 51022 catalogue documents 2 to 15 circuits; KONNRA documents 2P to 16P
3. Whether you need the housing only, the terminals only, or a loaded housing and a finished harness — the KR1252 bill of materials has no wafer, so the answer changes what you order
4. Wire specification — gauge and insulation outside diameter, because 1.25mm pitch with a 1.00mm jacket is a tight arrangement and the jacket diameter is not optional information here
5. Your load current, not just the connector rating — close to 1A in a high-position-count housing means the derated value is the one your design has to satisfy, and KONNRA publishes no derating table
6. Your circuit voltage, so the 125V-versus-50V question in KONNRA's own documents can be resolved against your application instead of left open
7. Your operating temperature requirement, because the Molex housing is documented to +85°C and the KONNRA part to +105°C
8. Application and annual volume
9. A drawing or photo, if the part number is unreadable

With those, four things get confirmed against Molex's own documentation: the position count, the wire gauge the terminal is validated for, the insulation diameter window, and the plating construction you need. Those four are where a board-in cross-reference most often goes wrong.

How to tell whether the part in your hand is board-in

1. Count the parts in the connection. If there is a separate pin block soldered to the PCB that the housing pushes onto, it is wire-to-board, not board-in.
2. Measure the pitch. 1.25mm points at board-in (51022), PicoBlade, CLIK-Mate or PanelMate — it does not distinguish them.
3. Check the orientation. Board-in housing and terminal are both documented as vertical, so the wire exits perpendicular to the board.
4. Count positions. Molex's 51022 catalogue runs 2 to 15 circuits.
5. Look at material and colour. Molex: Polyester, Natural. KONNRA: Nylon66 with UL94V-0, White.
6. Check whether there is a latch. Board-in is the branch that is not designed for repeated unmating, so a prominent positive lock points at a different family.
7. Read the part number. 51022 = board-in housing · 50061 = 28–32 AWG board-in male crimp terminal · 50080 = 26–28 AWG board-in crimp terminal · 797581062 / 797581063 = PicoBlade board-in pre-crimped leads.

Full technical write-up: Molex MX1.25 Board-In Connector Complete Guide

Disclosure: I work with KONNRA, which manufactures the KR1252 cross-reference. The Molex board-in figures above are taken from Molex's published part documentation for the 51022 housing and the 50061 / 50080 terminals; the KONNRA figures are from our published KR1252 product documentation and specification PS-KR1252-01. Where the two disagree — or where one source contradicts itself — I have flagged the difference rather than averaged it, and where a parameter is not stated in the sources reviewed, I have said so rather than filling the gap.

https://konnra.com/molex-mx1-25-board-in-connector-complete-guide/
Dongguan Konnra Electronics Co., Ltd