man I wish I could tell you. but I'm not home for a while and my feeble mind forgets.
but I believe it was a #21 bit and 10-32 tap. The directions for the T/C peep should tell you. in the mean time I will try to find out.
to be sure what size screw it is, go to a hardware store and find what size the mating nut is then go from there.
Be sure to go slow with the tap so it doesn't jam up or break. and use plenty of cutting oil. I found that the foaming type is great because it doesn't run all over.