Most AR barrels are sold with threaded muzzles to accept muzzle devices, the alternative is a barrel with a target crown, similar to handgun barrels. Check out our Muzzle devices here. On .223 and 5.56 barrels the thread pitch is most usually 1/2 x 28 which means that it's a half-inch diameter with 28 threads-per-inch. Muzzle devices have many uses which are covered in-depth on the muzzle device category pages buyers guide. Now that you have learned all there is to know about AR-15 barrels, you should feel confident in your ability to select the right barrel, with the right features to be the best AR-15 barrel for your money and your application.