BCM Pistol Receiver Kit Features This kit contains all the necessary parts to mount your AR15 M16 M4 Pistol Lower Receiver. Pistol receiver extension (buffer tube). This kit is compatible with the ATF compliant SigTac SB15 type pistol stabilizing brace. BCM Pistol Receiver Kit Specifications 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. BCMGUNFIGHTER QD Receiver End Plate Lock Nut (Castle) M4 Action Spring Carbine Buffer Assembly Carbine (options for H H2 H3)