Bcm pistol receiver extension kit w/buffer/spring/hardware FEATURES-Pistol Receiver Extension Kit-Buffer Tube-For AR15 Pistols -For your AR15, M16, M4 Pistol Lower Receiver. Pistol Receiver extension (buffer tube) machined from 7075T6-Hard Coat Anodized per Mil-A-8625F, Type III, Class 2-1.2" outside diameter. Will fit your ATF compliant SigTac SB15 type pistol stabilizing brace. Works with carbine buffer and action springs. Other Features: Pistol receiver extension receiver end plate, lock nut (castle) m4, action spring carbine, buffer