The knobs I chose for this project are very special: they are knobs from the original Atari 2600 paddle controllers! I bought them at All Electronics in Van Nuys many years ago, and there probably won't ever be a way to source them again. The prototype of Twister is a one-off!
It was really hard finding potentiometers that would fit the holes in the knobs, and even the rather expensive pots I did find had rather short shafts. The plastic knobs have metal bits inside to grip the shaft, but they are shoved too far up to work on these pots, and they ultimately get in the way.
So I chiseled them out with a screwdriver and wrapped the shafts with blue painter's tape until the knobs had a good friction fit.