This is a golden oldie.
About a billion years ago, I’d make special valve caps for presta valves from small dice, either six or 10 sided. Dice on tire valves is an old hot rod trick. It then got adopted by the BMX kids. It never quite made it from Vg8 to Vg5,2 Shrader threads. I fixed that along with scaled down dice.
I needed to make some more. I figured I’d draw it up and share the detail.
The angle that the die has to be held is fun. It’s less obvious than would be assumed. To cut the thread diagonally across the die, it is held at two angles. The first is simply 45 degrees (ATAN (12/12). The second is 54.74 degrees (ATAN(SQRT(2*12^2)/12)).
Then the only challenge is drilling and threading as deeply as possible into the die as possible without breaking it.
