LBE Unlimited is a quality manufacturer of AR-15 parts and accessories. This particular item is an AR-15 Mil-Spec diameter carbine receiver extension. This buffer tube can be used as a replacement unit or as a spare for a new build. This unit come pre-threaded standard and features 6 position notches. Features: Colt gray finish AR-15 Mil-Spec diameter recoil buffer tube Carbine receiver extension Pre-threaded