The thread PITCH of an asa thread is the same but the pipe thread fittings are tapered and the ASA is a STRAIGHT thread. It can bind up and ruin some gear. You can also have a great deal of difficulty getting it to NOT LEAK.
My LAW and Cannon used a T or 4 way 1/2 NPT galvanized pipe fitting as an air intake manifold. The standardard paintball ASA threaded regulator screws directly into the fitting. But the fitting has to be MODIFIED because of the tapered thread in the fitting. Otherwise you permanently screw up the soft aluminum thread of the reg or ASA fitting. Trying to 'tighten' it to not leak is a HUGE mistake.
I use a standard 1/2" NPT tap to convert that tapered thread to a "mostly" straight thread by taping the threads in the fiting ALL the WAY up to the top of the shank of the tap. Because the tip of the tap extends 2 inches or more into the fittings, you are limited to one end or the other of the T fitting. Kind of a cut and fit operation until your asa fitting or reg will screw in finger tight without binding up and seat on the shoulder of the fitting. Now you have the thread adapted, but unfortunately it will not seal and hold air.
So again you have to modify it a bit more. You have to make sure the top of the galvanized fitting is flat, smooth, and most importanly square. They can be very rough and irregular. But a little work with a flat metal file or grinding wheel gets the job done shortly.
Then I use one of those hand drill grinders with the 45 degree stone and grind a small chamfer inside that 1/2 tread. You want it just enough you can seal an O ring between the fitting and the shoulder on your reg or Adaptor fitting. Then you have a good seal. If the O ring is too fat, it can blow out and leak under pressure. Too skinney and it won't seal. So pick your O ring and then grind to fit. Definately a cut and fit operation. Rule of thumb, if you can FEEL the O ring start to compress AND you can screw it down to the shoulder with your FINGERS, you have the right fit. Lube the ring.. Now you are set. If you did it right you can install it to work and swap regs without any problems. I snug mine down a bit just to make sure the reg doesn't back out but I really don't think I need to. That compressed O ring provides plenty of friction to prevent backing out.