HMX FJ400 50g Linear

Quick Summary

The HMX FJ400 is a medium-weight linear that prioritizes a straightforward, drama-free typing experience over gimmicks. With a 50g actuation, a polycarbonate top over a P2 nylon bottom, and HMX’s well-regarded manufacturing tolerances, it lands as a dependable everyday linear that feels far more refined than its price suggests. It’s a strong pick for builders who want clean, smooth keystrokes without buying boutique-tier switches.

Specs and Feel

This is a true linear — no bump, no click, just a uniform glide from top to bottom. It actuates around 50g and bottoms out near 58g on a 22mm single-stage spring, giving a smooth, gently progressive press that suits long typing sessions and gaming alike. Travel runs to roughly 3.8mm total with a standard 2.0mm pre-travel, so the keystroke feels a hair shallower than a deep MX-spec switch, which gives a quick return.

Smoothness is the headline. HMX’s tight tolerances keep stem wobble low in both directions, and the factory lube does a good job suppressing scratch, so the stroke reads as consistent rather than gritty. The polycarbonate top paired with the P2 nylon bottom gives a rounded, slightly muted acoustic (a balanced thock-leaning sound rather than a bright, hollow poly clack) that flatters most plate and case combinations.

Tuning

You don’t need to do much here. The factory lube is competently applied, so most builders can run these stock and be happy. If you’re chasing the last bit of polish, a light hand-lube on the rails and a thin coat on the springs will smooth out any residual spring crunch; films are generally unnecessary given how snug the housings already fit.

Verdict

The FJ400 is an easy recommendation for anyone who wants a smooth, well-behaved linear without overthinking it: first-time builders, budget-conscious enthusiasts, and anyone assembling a quiet daily driver. It is not for someone hunting for an aggressive, marbly signature sound or an ultra-light feather switch. As a clean, low-wobble, factory-ready linear, it punches well above its modest cost. Easy pick.