I have a assortment of potentiometer and switch nuts from various electronic projects over the years. I found one that was just almost able to slip onto the very end of the plastic, then I gave it a few turns with a pliers to force it to thread onto the plastic so it won't slip off.

I'm pretty sure the size I used is 1/2"-32 though I don't have a thread gauge to actually measure it with.

Attached Thumbnails