This machined steel adapter has detent locking notches and is finished in durable black oxide. It enables you to shoot your .223/5.56 AK through a 1/2x28 threaded muzzle brake, fake suppressor or real suppressor. Threads from AK-47 (14x1LH) to 1/2x28. (.223/5.56) only, adapter not large enough for 7.62x39 round. Inner Diameter is .335"