there are two common thread measurements you will come across on most pb guns. one is 10-32, often used on grip frames, drop forwards, etc. the other is 1/8-27 NPT. this is for air fittings. most likely your macro or stainless steel fittings are 1/8-27 NPT, unless they are metric.
if you want to drill and tap either of these holes, you'll need:
a 21/64 drill bit
, 1/8-27 NPT tap
, and the proper tap wrench
for the air fittings, and 10-32 tap
, 5/32 drill bit
, and the proper tap wrench for the grip frame type holes. you will most likely be tapping an aluminum part, so you will also need aluminum tap fluid.
to tap a hole is simple. just drill the hole in the correct spot, put the tap in the wrench, secure the part you're tapping, insert the end of the tap into the newly drilled hole, make sure the part and the tap make a 90* angle on all sides so it's even, and slowly screw the tap into the hole. every turn in, turn it out a quarter turn to break the chip you just made. continue to desired depth.