I'd use Steve also.
If it were me, I'd have it threaded 1/2x36.
That's the std. for 9mm & what YHM uses.
Not sure what Berretta does at the factory, but this will keep you from having to use an adapter.
Have Steve make a thread protector for it while he's threading it.
IMO, 1/2-36 is more common on rifles to keep people from screwing 223 flash hiders on them. 1/2-28 is more common on pistols from what I've seen.
It really depends on what thread pattern the thing is coming with. They offer QD pistons in 1/2-28, 1/2-32, and 1/2-36 and it probably comes with one. I would still do 1/2-28 and get the right piston. I've never once found myself saying I wish my stuff was threaded something besides 1/2-28 (besides 13.5-1LH).