Steve B wrote:
It's a standard/coarse thread 9/16" hole, 15/16" total outside nut. The
damn nut is bigger than a walnut, so there's going to be a little
work welding a cap in there, then trimming it all down to a workable
size. I'll go to Ace and see if they have a thinner one that
requires less machining.
For what I charge, I could just go buy a new opener. Good thing this
isn't for a real customer.

Why do we do that?

i have this same opener. it looks like it should be a standard nut. did you
try all those little boxes at an ace hardware?

seems i see these in yard sales a lot. buy another broken one for another $2
just for the nut.