Switch Anatomy
The five parts inside a mechanical switch, what each one does to the sound and the feel, and which ones you can change.
A mechanical switch has five parts. Open one up and you can lay them out on a desk in about four seconds, which makes it one of the few things in this hobby you can genuinely understand completely.
This page is the component reference. If you want the specification sheet and how to choose, switches covers that instead.
Top housing
The lid. It clips onto the bottom housing, holds the stem in its channel, and takes the impact when the stem comes back up.
The top housing is responsible for the upstroke sound, and it is the part people underestimate. When a switch is described as clacky, that is usually the stem hitting the top housing on the return, not anything happening on the way down.
It also sets how much the stem can rock side to side. The channel is molded slightly wider than the stem so the two do not bind, and that clearance is stem wobble. Tighter tolerances mean less wobble and a more solid feel, and they are the main reason two switches with identical published figures do not feel identical.
Most top housings are polycarbonate or nylon. Polycarbonate is harder, so the upstroke is brighter and louder; nylon absorbs more, so it is duller and quieter. Many switches use a polycarbonate top with a nylon bottom specifically to get a bright upstroke and a deep downstroke.
Bottom housing
The base. It carries the two metal pins that pass through the PCB, holds the metal leaf, and has a central pole the spring sits on.
The bottom housing takes the downstroke impact, so it does most of the work on the sound people actually notice. A nylon bottom housing is the usual recipe for a deep sound; a polycarbonate or POK bottom is the usual recipe for a sharp one.
Underneath, the two metal pins are the electrical contacts. Some switches add two plastic posts either side, which locate the switch more precisely in a PCB drilled for them. Two pins alone is a three-pin or plate-mount switch; with the posts it is five-pin or PCB-mount. The posts can be clipped off with flush cutters if your board does not have the holes.
Stem
The moving part, and the one that determines the feel.
The top is a cross, which is the MX standard that keycaps push onto. The bottom sits on the spring. The important geometry is on the sides: two legs that ride against the metal leaf as the stem travels.
On a linear, those legs have a smooth, straight profile, so the leaf is pushed aside gradually and you feel nothing in particular. On a tactile, the profile has a step in it, and forcing the leaf over that step is the bump. The bump’s size, sharpness and depth are entirely a matter of how that step is shaped, which is why “tactile” covers everything from a faint rounded rise to something that feels like a fault in the key.
The stem is also the part that slides against plastic for its whole travel, so its material sets the smoothness. POM is the overwhelming favorite because it is self-lubricating: 35 of the 45 switches in this index that publish a stem material use it. Newer switches sometimes use UHMWPE or a UPE blend, which are slipperier again and pitched differently.
Two variations worth recognizing. A dustproof stem has a skirt around the cross that closes the gap into the housing, which keeps debris out and slightly changes the sound. A long-pole stem is extended so it reaches the bottom housing sooner, which shortens the total travel and gives a much sharper, louder bottom-out. Long-pole switches are how most of the current generation get their crisp sound, and it is why so many switches now list 3.5 mm of travel rather than 4 mm.
Spring
A coil around the bottom housing pole, holding the stem up and pushing it back after a press.
The spring sets the weight, and it is the easiest part to change. Springs are sold loose in every weight from roughly 35 gf to 80 gf, and swapping them turns a switch you like into a switch you like at the right weight.
Three kinds are worth knowing:
- Linear springs get heavier at a constant rate as they compress. The great majority of switches use these.
- Progressive springs get heavier at an increasing rate, so they feel light at the top and firm noticeably near the bottom. Good if you want a light press but a clear floor.
- Long springs are longer than standard, so they are already slightly compressed when the switch is at rest. That raises the force needed to start the press and makes the return faster and more insistent.
Spring material and finish matter less than the hobby sometimes claims, but they matter for one thing: an uncoated spring can produce a faint metallic ringing during the return, called spring ping. Gold-plated and stainless springs ping less, and a drop of thin lubricant on the spring ends stops it almost entirely.
Metal leaf
The part that actually registers the keypress, and the only part you should not touch.
The leaf is a folded strip of springy metal, usually a copper alloy, sitting in the bottom housing with two arms held slightly apart. The stem’s legs hold one arm back. As the stem descends, the legs let that arm go, the two arms touch, the circuit closes, and the keypress registers.
Everything else in the switch is about feel and sound. The leaf is the switch’s actual job. It also explains two things:
- Why actuation happens partway down. The leaf closes when the stem’s profile lets it, which is a fixed point in the travel. Pressing further does nothing electrically.
- Why lubricant must not reach it. Grease on the contact surfaces can stop the circuit closing reliably, so the key becomes intermittent. When lubing a switch, the stem rails and the spring get lubricant and the leaf does not.
The leaf is also where a clicky switch’s noise comes from, in one of two designs. A click jacket is a loose collar around the stem that the stem catches and releases, which snaps against the housing; Cherry MX Blue works this way. A click bar is a separate sprung wire in the bottom housing that the stem snaps past, giving a sharper and louder click on both the press and the release; Kailh’s Box Jade works this way.
The part that is not a part
Switch films are thin gaskets, usually 0.15 mm to 0.3 mm of polyethylene or silicone, placed between the top and bottom housing before they clip together.
They do one thing: take up the slack in a loose housing fit. Because switch housings are injection-molded to a tolerance, some pairs clip together tightly and some rattle. A film makes the join solid, which reduces housing wobble and usually deepens the sound slightly.
Films are worth it on switches with loose housings and pointless on switches that already fit tightly. There is no way to know which you have without opening one, which is a fair summary of most switch modification.
What you can change, in order of effect
- Lubricant on the stem rails and spring. Biggest change for the least money, most tedious to do.
- Spring. Changes the weight without changing the sound or the feel of the bump.
- Film. Only helps if the housing was loose to begin with.
- Housing swap. Putting one switch’s stem in another’s housing is how a Frankenswitch is made. The Holy Panda is the famous one: a Halo stem in a Panda housing.
Browse the switch index for the housing and stem materials of specific switches, or switch lubes for what to put on them.