I am quite sure that it is 1/2-28 that you want. I have a CZ 455 on which I put one of their "compensators" 1/2-28 are the most commonly available, however my barrel, a CZUB, had 1/2-20. I did eventually find one.
Mine gave me a bit of extra weight out front, which it needed, and being the same diameter as the heavy barrel looks great. I found no perceptible change in accuracy, either good nor bad.
People say that these compensators "strip" super sonic gas away from the projectiles. Who knows, I don't.
What I do know is that it seems to have made my rifle quieter (not what I expected). My friend and I often shoot 100 yards side by side. He has a 455 with a CZ-USA barrel (1/2-28 thread) with no compensator. We both shoot TAC-22; his rifle is at least 50% louder than mine. He is a bit better shot than I am but groups are comparable. most days.
CZ Compensators are inexpensive. I just looked, now everyone has 1/2-20 in stock and no 1/2-28s. LOL, Tesro has them for $35.00, Thread adaptors are not expensive.