Our AR15 .223/5.56 Bull barrel thread protector should fit all standard .936 barrels with a standard 1/2"-28 that are factory threaded for a flash hider. This protector can be used in place of your muzzle brake, flash hider, or suppressor so your barrel won't get damaged when not in use. Made of all Steel construction with a Black Nitride finish. Includes a crush washer.