This is a list of the more common thread associations. If you have one of these, then the threads are probably what is stated here. This is by no means exhaustive or guaranteed. There is nothing that forces Gun A to have Thread A. You should always double check. There is always a chance the barrel was originally un-threaded and someone put who-the-hell-knows-what threads on it. Guns that don’t come from the factory threaded, or at least with that option, are likely to be unguessable. You’ll just have to find out the old-fashioned way. Yes, I just made up the word “unguessable.”
AR-15 .223/5.56mm – 1/2-28
AK-47 – M14x1LH
AR-15 9mm – 1/2-36
AR-15 RRA .458 SOCOM – 5/8-32
AR-15 WC .458 SOCOM – 11/16-24
AR-10 .308/AR-15 .300 AAC Blackout – 5/8-24
M14/M1A – .595-32
1911 .45 – .578-28, .575-40, or M16x1LH
Glock .40 (conversion barrel from larger caliber)/.45 Cal. – .575-40 or .578-28. Can be M16x1LH (or some other weird stuff) if euro barreled
Glock .40 – 9/16-24
Glock 9mm – Mostly 1/2-28, but sometimes M13.5x1LH if euro barreled
FN FAL Inch (L1A1)/MP-5/M1 Carbine – 9/16-24, maybe? Sometimes?
FN FAL Metric – 9/16-24LH (occasionally these are off-the-wall metric, but that’s pretty rare. My STG-58 is 9/16-24LH)
HK SOCOM Mk.23 – M16x1RH, weirdos…
Walther P22 – M8x0.75 recessed
GSG 1911 .22lr (and the SIG copy) – M9x0.75 recessed
Umarex .22lr rifle, and the assorted rebranded versions thereof – M8x0.75- the Walther P22 adapter would work, but odd
SIG Mosquito – M9x0.75
SIG P220 .40/.45 – .578-28
SIG P226 – M13.5x1LH
HK G3/53/HK91/HK93/PTR91 – M15x1
Cobray/MAC/etc… M-11/9mm and most clones – 3/4-10
Steyr AUG – M13x1LH
Yugo PAP/MPAP/92 w/ “big weird threaded thingy” – M26x1.5LH
AK-74 w/ “big weird threaded thingy” – M24x1.5RH
If you have something odd or unguessable, please don’t ask me to guess, too. I’m some dude on the Internet. How can I possibly have more information than you, the owner, who is holding it in his hand? Guessing in person is better than guessing over the Internet. I’ll try to help where I can, but don’t get mad if it’s wrong. I have no idea how many fingers you are holding up right now… Maybe just the one in the middle? ;-)
If you have any additional information or corrections, feel free to post a comment.
“I need a screw for my car. It’s a blue car with tires. WHY WON’T YOU HELP ME!!! YOU SUCK I HATE YOU!” Would you really expect any non-telepathic person to figure that out? I’m trying to help, but you gotta give me at least a rational hint…
“I wish you would just tell me. Why do you have to make it so hard, I’m trying to give you my money!” I wish there were a simple answer, but there isn’t one. I could lie to you… Nah, I couldn’t.
I’m not the one who made it this way. A world full of jerks who want you to have to buy special threads at $[too expensive] from them made it this way. I’m trying to undo it. There are tons of ridiculous threads out there, and none of them have any rhyme or reason, many have no published specs at all. They’re just plain made-up. Others are done poorly by a drunk guy on a sloppy manual lathe and don’t fit what they claim to be. There’s a world of crap out there…
Here’s an excellent example. Mk23. M16x1RH. The same company makes plenty of guns with the normal M16x1LH. Why did they do the Mk23 backwards? It’s the only one in the world like that, and it even defies their own conventions because they make plenty of other guns that have to proper thread…
There are standards and then there are “common conventions.” There are no standards that dictate a certain thread on a certain make/model/caliber of gun. There are common conventions, but there’s no guarantee that they were followed on your gun.