Retraction: The information below does not actually apply to KK caps. Sorry if I got anyone's hopes up.
Also, fun fact for those of you who might up getting topre, but wanted MX.
TIL, apparently, topre stem caps can fit on MX stems. I'm not sure if this is common knowledge or if this is just a weird thing with this particular cap.
I just found out with a topre keycap that was an given as an extra in the most recent KRAP sale. I wouldn't put it on a key that I use frequently or on a board that travels ... but if it's just sitting on your desk, it should work just fine. It is able to move side-to-side a bit, but it's surprisingly snug.
Just sharing because I didn't know it before just now and I likely would only somewhat reluctantly have bought a topre cap.