This is our standard AR-15 Micro Gas Block. Designed with the minimum profile to fit under nearly any quad rail system, it snugly fits standard .875 diameter barrels. Features: Mil-Spec dimensions .875 diameter Hardened Steel construction Non-reflective, Matte Black finish Includes roll pin, 2 set screws and allen wrench Note: Not designed for bull barrel mounts Fits: AR .875" barrels