Front block screw is 9/16-24 it's a specialty tap you would probably have to buy separately.
If you're mining a gun I'd suggest using the threads already there as a guide to tap the body deeper before you hack the front of it off. Everything else should be the same as any other tap: One turn in half a turn out, with lots of lube. Pulling the valve beforehand is optional but probably worth doing as it will need to be pulled out of be cleaned anyways.
Lastly assuming you're mining a 'cocker; the mini block's on compulsive won't fit standard bodies (with my experience on a 2k2) without a little filing or a trip over to the mill.
Originally Posted by pillage
The Cocker Haiku:
It worked before?
Screwed with it didn't you.
Got what you deserve.