View Full Version : thread size of standard AR-15 barrel

December 26, 2009, 01:40 AM
Hello I have a problem I want to buy new upper for my M4 type AR-15 rifle and i need to know the standard thread size of the barrel so that i can when i order my muzzle break I get the correct size I do remember that i read somewhere that it was 1'2'' by 28 threads for the .223 cal. also is that the same size for 6.8 AR type rifle. Thank you for your assistance with this problem.:cool::cool::cool::cool:

December 26, 2009, 04:16 AM
Yes, they are 1/2"x28

ETA: this applies to .223 and 5.56

December 26, 2009, 05:45 AM
Not always 1/2"x28... I'll have to do some digging, but I've seen 6.8 bbls with threads in the 9/16" ballpark. I'm pretty sure my RRA is one of the later with the 9/16" ballpark-ish threads.

December 26, 2009, 07:04 PM
Most 6.8s are 5/8"x24.
308s are also 5/8"x24.