The primary started out being wound between wooden teeth cut in pine.
Then, on the list I read that wood may not be the best insulator for the currents involved, so I drilled holes for nylon bolts, inserted the bolts, then popped out what was left of the teeth.

Next time, I can skip making the teeth altogether and start out with plastic bolts.
It uses 16 turns of 1/4" fridge tubing spaced 1/4" apart (1/2"on center).

The bolts are 1" long x 1/4" diameter.

The bolts...  predrilling 1/4" holes made inserting these things a breeze!  I couldn't quite push them in, and didn't want to bother turning them, so I hammered them and it went very quickly.  They came from