The Bravo Company Receiver Extension Buffer Tube if 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.