Journal · Shop Notes

Brass vs aluminum: why weight changes how a key sounds

Shop Notes, from the Key Bored workshop · October 18, 2026 · 3 min read

Brass is roughly three times as dense as aluminum: around 8.5 grams per cubic centimeter against 2.7. Put brass inside a keyboard or a single key and it gets heavier, the sound usually drops lower, and the whole thing feels planted in a way that's hard to describe until you've held both.

What mass does to sound

When a key bottoms out, the switch stem slams into its housing and the impact travels into whatever is holding the switch. A light body moves a little and rings. A heavy body barely moves, so less of that energy turns into a high, hollow ring.

You hear it as depth. The same switch in a light plastic shell sounds clacky and bright. In a heavy body it sounds rounder and lower, closer to what enthusiasts call a thock. That's the main reason so many premium keyboards bolt a brass or steel weight to the bottom of the case. Some of those weights are purely there to make the board heavy, and nobody complains.

What aluminum is good at

Aluminum is light, stiff, and very easy to machine to tight tolerances. A CNC mill can cut it quickly and cleanly, which keeps costs reasonable and edges sharp. It also takes anodizing, which lets you color it almost any shade with a finish that's part of the metal rather than painted on. We wrote a whole piece on how anodizing works.

The alloy matters. 6061 is the everyday choice. 7075 is a stronger aerospace alloy that holds crisp edges and takes a beautiful anodized finish. It costs more, and in a small object you can feel the difference in how precise the edges are.

What brass is good at

Brass is heavy, it machines beautifully, and it looks warm in a way aluminum doesn't. Free-machining brass like C360 cuts cleanly into fine details and threads, which is why it shows up in everything from instrument parts to watch components.

It also changes over time. Handled brass darkens into a patina, a little uneven and very personal. Some people polish it back to bright. Others wouldn't dream of it.

Why the best designs use both

Aluminum on the outside, brass on the inside, is a common pattern for a reason. The aluminum gives you color and precision where people look. The brass gives you mass where it does the most good, low and close to where the switch is held.

That's the layout of the KB OneKey Pro. A solid brass weight slides up into an anodized aluminum case, and the switch clips into the brass itself, so every press lands in solid metal. Four Torx screws thread straight into the brass and hold the two together. The brass makes up most of the underside, so you see it every time you flip the key over.

Living with each one

Anodized aluminum asks very little. Wipe it with a soft cloth, use mild soap if it gets grubby, and keep it away from oven cleaner and other strong alkaline products, which can eat into the anodized layer. That's about it.

Brass is more of a relationship. Skin oils darken it unevenly at first, then it settles into a deeper, more even tone. If you want it bright again, a little metal polish brings it back in a few minutes. If you like the patina, do nothing. A brass weight that has spent a year on someone's desk looks like it belongs to them, and we think that's the best argument for brass there is.

When lighter is better

Heavier isn't automatically better. A heavy key is less pleasant in a pocket and can feel dull if you like a bright, crisp sound. The KB OneKey is the light option, about 10 grams of solid polycarbonate, with an air chamber under the switch tuned to keep the sound crisp instead of hollow.

If you want something you'll carry everywhere, go light. If it lives on a desk, or if the sound is the whole point for you, go heavy.