Can anyone advise the thread size for the end of the AR-15 barrel?  I want to have a muzzle break manufactured.

Thanks

Standard thread size is 1/2x28 NEF (half-inch diameter, 28 threads per inch, National Extra Fine pitch) class 3a. I'm not sure of the length, I think it's 1/2 inch also. Try KurtsKustom in the Industry Forum.
Happy hunting,
havoc

A clarification here:

You can't thread an unthreaded barrel UNLESS the threads won't mate to ANY flash suppressor.

Then, if it's threaded, I THINK the accessory must be permanently mounted -- pinned, staked, or soldered.

Bushmaster makes two brakes for post-ban guns. They pin in place and need installation. Bushmaster will install them for you.

The BATF can't tell you the difference between a "suppressor" and a "brake." Like "pornography" . . . "They know it when they see it."

A brake can be a fairly sophisticated design issue. Lots of after market options available.

Thank you for the info, but the rules are a little different here in Canada.  I can thread the barrell, as the rifle is classified a handgun here, and as such is a restricted weapon.  It came with a threaded barrel, however I just want to shorten it, and have a new brake made.