Steel adapter allows you to install muzzle brakes and flash hiders on an AK -47 tactical rifle with an un-threaded barrel. No machining necessary; four setscrews secure adapter to barrel in seconds. Adapter features 14mm-1.0 (LH) left hand threads for 7.62x39 caliber AK-47 and SKS rifles. Outside diameter of the barrel must be .54 or THINNER to fit into the adapter. Adapter hole for the bullet is only .343"