Anyone know the best drill bit size for the Jerry Fisher grip cap screw?

I do not know the size drill bit, but I do remember folks advising to buy an extra grip cap screw and weld a bolt head to it and turn it into a "tap" to keep from harming the delicate screw heads.

Talley sells a tap, they call it a pilot, that forms the the threads for the screw used on the Fisher cap. Pre-drill, then run the pilot in/out with a cordless drill and the screw install is easy with no messing up the slots. I use a little Chapstick on the threads for lube. Get the perfect fitting screw driver tip, Brownell's sells them. I think I use a #31 drill bit but would have to look on the bench to confirm.

After some trial and error, a 11/64 brad point bit seems to be about perfect for the fisher grip cap screw.

Also, an Allen head screw with 12-24 threads works like a charm to tap the threads: https://www.mcmaster.com/92196A261/

Can't you just use a tap?

I have a couple of the taps, they work quite well