Rick, most different calibers do have different threading. But it's far easier to get the one that is the "most" common from the start. That's why I recommended the 1/2-28.
There are a lot of suppressor manufacturers, and a lot of differences between them, so I won't go into specifics on each one, but to make a long story short, 1/2-28 on a 9mm suppressor would be the most ideal thread for a few reasons. And I'll even go one further and recommend you look into the Huntertown Arms Guardian 9mm suppressor for the baffle type, AND the low cost. Or also check out the Thompson Machine brand of suppressors. You get a lot for your money at either place.
While you wouldn't be able to use the suppressor on 223, but you would be able to use a 9mm suppressor on a 22LR converted AR, a handgun from 9mm down to 17 hmr like a Sig Mosquito or Walther P22 with the correct thread barrel adapter, or a host of other guns like an HR 38/357, MP5, uzi, glock or xd or M&P Storm lake threaded barrels, etc.
And of course, you can always get thread adapters so you can use the 9mm suppressor on a 300 subsonic blackout or on anything else that is within the strength rating of the suppressor that isn't threaded the same, but 1/2-28 is the most common and why I recommended it.
I have a bunch of different thread adapters like 14-1 LH for the SKS bullpup and AK's, etc., but like I said the 1/2-28 is the most common.
Just note that I built my 9 mil can strong enough to handle rifle or pistol cal's
I was going for uni-versal-tility when I built it so that's why I mentioned that commercial 9mm suppressors generally won't handle full house rifle pressure because they built them from aluminum and other things to keep them LIGHTWEIGHT, rather than robust.