KK 254 2.54mm Pin Header & Connector System — Molex's Workhorse Wire-to-Board Interconnect

If you have ever plugged a fan header onto a motherboard, connected a front-panel USB cable, or wired up a benchtop prototype on 0.100" perfboard, you have probably touched a Molex KK 254 connector without knowing it. The KK 254 series is Molex's 2.54 mm (0.100 inch) pitch wire-to-board and board-to-board interconnect system, and with 367 active variants it covers everything from a basic 2-pin friction-lock header to a 28-circuit polarized housing with crimp terminals and pre-assembled cable harnesses.

At its core, KK 254 solves one problem: getting signals and low-current power from a wiring harness onto a PCB, repeatably and without soldering each wire directly to the board. The 2.54 mm pitch means you can drop these headers into standard 0.100" grid layouts — they sit naturally alongside DIP ICs, resistor arrays, and breadboard-compatible modules.

What you get with KK 254

The system splits into three pieces you mix and match:

• PCB headers (vertical or right-angle, tin or gold plating, through-hole or surface-mount). Vertical headers with friction ramps are the most common — the plastic housing snaps onto the header and the ramp resists vibration so the connector does not walk off the pins.
• Crimp terminals (Series 2759 for 22-30 AWG, Series 41572 for 18-24 AWG, both available in tin and select-gold). These are the part you crimp onto each wire. Gold is worth it if your device lives in a humid or condensing environment; for an indoor appliance, tin is fine and costs half as much.
• Housings (single-row up to 28 circuits, polarized with a keying rib so you cannot plug them in backwards). The housing captures the crimped terminals with a plastic lance — once the terminal clicks in, it stays. Extraction requires a $3 tool (part 11-03-0043) but you will only need it during rework.

Where you see KK 254 in the wild

• Desktop PC and server motherboards — front-panel headers, USB 2.0 internal headers, fan headers, and RGB LED strips all use KK 254 or a mechanically compatible clone. The friction lock is what keeps your power-button connector from falling off during assembly.
• Home appliances — washing machine control boards, microwave display panels, and air-conditioner indoor units. These are cost-sensitive designs that pick KK 254 over more expensive latching connectors (like Molex Mini-Fit) because the board is mounted in a fixed enclosure and does not need a secondary latch.
• Industrial controls — PLC I/O modules, sensor junction boxes, and DIN-rail terminal-block adapters. The right-angle header variant lets you bring connectors to the edge of the board inside a slim enclosure.
• Test & measurement — benchtop instruments, data loggers, and development boards. KK 254 mates directly with standard 0.100" pin headers, so you can plug the same housing onto a KK header or a generic breakaway pin strip during prototyping.
• LED lighting — constant-current driver boards use the 2-circuit housing for DC input, and multi-channel LED controllers use the 4-8 circuit variants for RGBW/RGBCCT channel outputs.

How KK 254 compares

Vs. generic 0.100" breakaway pin headers: Generic pin strips have no polarization, no friction lock, and no retention ramp. If you ship a product with a generic header, the connector can be plugged in backwards at the factory and the board comes back as a warranty return. KK 254 housings have a physical key that prevents reverse insertion.

Vs. Molex SL (Series 70430, also 2.54 mm): SL is a latching connector — it has a positive latch that you squeeze to release. KK 254 uses friction only. SL costs more per mated pair but is the right pick when the connector faces outward on a panel and someone might pull on the cable. KK 254 makes more sense for internal connections inside a closed chassis.

Key specifications at a glance

How to pick the right variant

Start with the circuit count. KK 254 housings are not stackable end-to-end like some Hirose or JST series — if you need 16 positions, buy a 16-circuit header and housing, not two 8s. Count your signals, add one spare ground pin, and that is your circuit count.

Pick tin vs. gold. Gold is about 2-3x the per-contact cost. It matters when: the device operates outdoors or in an unheated warehouse (condensation corrodes tin), the connector may sit unmated for months during storage, or the mating cycle count exceeds 25 over the product's life. For a TV that gets assembled once and never touched again, tin is the right economic choice.

Choose orientation early. Right-angle headers let you lay the wires flat against the board — important in 1U rack enclosures and slimline gear. Vertical headers pack more circuits per square centimeter of board area but add to the Z-height. If your mechanical team has not finalized the enclosure, order samples of both and test-fit.

Crimp terminal gauge range. Series 2759 covers 22-30 AWG, Series 41572 covers 18-24 AWG. Check the actual wire you plan to use, not the gauge you wrote in the spec. A UL 1007 22 AWG wire with insulation is roughly 1.5 mm in OD; the terminal's insulation crimp barrel must close around it. Getting this wrong is the number one reason KK 254 assemblies fail a pull test on the first prototype run.

Procurement notes

Molex ships KK 254 in standard packaging: headers come in bags (small quantities) or tape-and-reel (pick-and-place), housings in bags, and crimp terminals on reel. Minimum order quantities are typically 100 for terminals and 10 for housings. Lead times on popular configurations (2-8 circuits, tin plating) are normally 2-4 weeks from distribution; odd circuit counts (13, 17, 19) and gold-plated variants can push to 8-12 weeks. Second-source equivalents exist from TE Connectivity (MTA-100) and JST (NH series) with the same 2.54 mm pitch, but neither is a drop-in mechanical replacement — the polarization rib profile and terminal lance geometry are different, so cross-sourcing requires re-qualification.