Seems you've solved your own conundrum. Hahah. .45 usually diverts to .578x28, as you pointed out. 9mm??? Mixed bag. In my 1911, the rifling is left hand twist, so a Right hand twist thread prevents the muzzle device from being worked off. At least impedes it. Lot of bang going on with a .45, and on a big tilt barrel like that, things are bound to move. Back to 9mm, a lot of them I see are right hand twist, so whatever the thread, might be opposite of your rifling twist direction. In US, probably going to be 1/2x28 as that is the same for .22 caliber, too, and easy to produce same thread on many different platforms instead of designating a thread for a single platform. Could also be something like M14x(whatever goofy metric they use for their threads per inch, forgive the "metric" pun... =-p).