I purchased the tap from McMaster.
I bored the hole to .631"
Took a while to tap. I started the tap in the lathe, then using a 12 point socket and a 1/2" ratchet, wet with Tap-Magic cutting fluid, a little in, then out, then reapplied cutting fluid.
Took a while.
I made these parts out of 4130 chrome moly.