I see that all the bench grinders and buffers have their spindles
threaded in UNF - either 1/2-20 or 5/8-18. Is there a reason for this?

I am asking because I just tried to cut a 1/2-20 thread on an adaptor
I made and could not do it - most likely because of the Crappy Tire
die. I do have a good 1/2-13 SKF die. OTOH it might be God's way
telling me to finally learn how to cut the threads on a lathe.

Before I do anything so heroic I thought I would ask...

Michael Koblic,
Campbell River, BC