The LBE AR-15 Mil-Spec 6-Position Buffer Tube is a stand-alone receiver-extension tube for AR-15 carbine builds. Use it as the foundation for a fresh build or as a spare in the parts bin for a stock swap. Fit: AR-15 mil-spec lowers and mil-spec diameter collapsible carbine stocks. Commercial-spec tubes are wider - do not use commercial-spec stocks on this tube. Features: 6-position adjustable length-of-pull range Mil-spec diameter - fits all standard collapsible mil-spec carbine stocks Hard-coat anodized aluminum with rolled threads for clean lower-receiver engagement US-made by LBE Unlimited This tube ships bare. You will need a castle nut, receiver end plate, recoil spring, and buffer to complete a stock assembly if you are building from scratch. Best practice: torque and stake the castle nut after install to prevent it from backing out under repeated cycling.