Do I need to insulate the center bolt securing a toroidal transformer?

Yes. Long ago before I learned, I used a piece of copper "all-around" in a loop to mount a big toroid. This of course made a very hot piece of copper, but I didn't notice for months besides thinking "Why is this PSU running so hot?" lol
 
I only use stainless bolts for mounting a toroidal. Fortunately all of mine are custom made with potting, so the bolt is also shorter and does not protrude out the top too much. With a flat and spring washer and a nylock nut, it is not going to go anywhere.
 
Last edited: