We've featured several keyboard switches based on the Kailh Box design on Tested because they're an exciting alternative to the classic Cherry architecture. Box switches exist with almost every weight and switch characteristics you can imagine, but they come with a drawback: we've learned in recent months that these switches can break some keycaps. There are retooled Box switches available now, so let's evaluate this fix.
Box switches have a completely different stem design compared to Cherry switches and Cherry-style clones like Gaterons. There's a wall around the cross stem that makes the switch water and dust resistant, and it stabilizes the switch to reduce wobble. The problem lies with the x-axis part of the cross—it's thicker than other switches.
The left-to-right arm of the cross on original Box switches is designed to be 1.32mm +/- 0.02mm. The arms actually jut out slightly at the end, which you can see in the image above. The switch on the left is original, and the right is retooled. Because there's always some variation, the +/- 0.02mm swing can make the old Box switches up to 1.34mm wide. You wouldn't think such a small change could cause problems, but it did.
Based on information obtained by NovelKeys, Kailh made this change at the behest of its first Box switch customer, which wanted the keycaps to be tighter. No one knew at the time there would be a negative impact on certain keycaps. Unfortunately, the keycaps most susceptible are also some of the most expensive and difficult to replace.
The slightly wider arm can warp the stem on keycaps, making them looser over time. It can even cause hairline cracks in the plastic that make the keycap prone to just popping off. This happens mainly with ABS keycaps, especially those with thicker walls. The 2mm-thick walls of GMK keycaps don't have a lot of flex, so the larger arms on the Kailh switches can wreak havoc with the keycap stem. I personally lost a spacebar to Box switches when this all came out several months back.
The fix proposed by Kailh is simple. Rather than making that part of the stem 1.32mm, it is now aiming for 1.30mm. Even with natural variance, you shouldn't have a measurement more than 1.32mm now. I've measured a few dozen retooled box switches, and they seem to tend toward even smaller measurements of 1.30-1.27mm. That's small enough to leave your keycaps intact without feeling loose.
When purchasing Box switches, make sure you know if they're retooled or not. All NovelKey's stock is fixed, but other retailers may still have old switches. If you have those, make sure you use PBT keycaps, which are less susceptible to stem damage.