Kailh Box Spring 40g
The Kailh Box Spring 40g is a 40g linear with a 20mm extended spring, IP56 waterproof Box housing, and a transparent light pipe for bright RGB.
How it feels
Feel ratings not yet recorded for this switch.
How it sounds
Full review
Quick Summary
The Kailh Box Spring 40g is a light 40g linear built on Kailh’s Box stem, wrapped in an IP56 waterproof and dustproof housing and fed by a 20mm extended stainless-steel spring. It is an unusually practical switch: cheap, factory lubed, splash-resistant, and topped with a transparent light pipe that throws RGB cleanly. If you want a featherweight linear that shrugs off spills and lights up well, this is an easy recommendation.
Specs and Feel
This is a true linear with no bump and a clean 1.6mm pre-travel down to a short 3.3mm total travel. The 40g actuation sits on the light end of the spectrum, so keypresses feel quick and effortless rather than deliberate. The 20mm extended spring is the standout: it keeps the return tension consistent across the stroke and gives the switch a livelier, more uniform feel than a stock-length spring, with less of the dead, mushy bottom that plagues some budget linears.
The Box stem design earns its keep here, with the cross-mounted leaf and self-cleaning contacts producing noticeably tighter stem stability than standard MX stems. Wobble is well controlled in both directions. Smoothness is good for the price thanks to the factory lube and the PC-top, POM-bottom housing pairing, which keeps scratch to a minimum. Sound is on the quieter, slightly clacky side typical of Box switches rather than deep or thocky.
Tuning
These really do not demand work. The factory lube is competent, and the Box stem resists dust intrusion, so most builders can run them stock. If you want the last bit of refinement, a light spring lube tames any faint ping, and a thin film of dielectric grease on the rails sharpens the glide further. Films are unnecessary given the snug Box tolerances.
Verdict
Buy these if you want a light, dependable linear that survives real desk life and lights up brilliantly. The waterproofing, extended-spring snap, and rock-bottom price make the Box Spring 40g a smart pick for RGB-forward and gaming builds. Skip it only if you prefer heavier springs or the deep, muted sound profile of POM-heavy boutique linears.
Frequently asked
Is the Kailh Box Spring 40g really waterproof?
Its Box housing carries an IP56 rating, meaning it resists dust and water spray, which makes it a sensible choice for spill-prone desks. It is splash-resistant, not submersible.
Does the 40g actuation feel too light?
At 40g it is a genuinely light linear, lighter than the typical 45-50g mainstream linear. Fast typists and gamers tend to love it, while heavy-handed typists may bottom out and trigger keys accidentally.
Does the Box Spring 40g need lubing?
It ships factory lubed and is smooth enough out of the box for most builds. A light hand-lube on the springs can quiet residual ping if you are chasing a fully polished result.
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