Bravo Company MFG MK2 Receiver Extension Mil-Spec AR15/M16/M4 Black. Machined from 7075T6 and manufactured to Mil-Spec dimensions and specifications. Mil-Spec receiver extensions have a slightly smaller dimension where the stock slides on. These tubes should be used with stocks such as USGI BCM Colt LMT SOPMOD VLTOR Stag Arms and others that a made to the Mil-Spec size. These receiver extensions can also be used on most AR-10s. NOTE: These buffer tubes require a M16 rifle action spring and specific BCM MK2 buffer carbine and rifle buffers will NOT work. Specifications for Bravo Company MFG MK2 Receiver Extension: Manufacturer: Bravo Company MFG Color: Black Finish: Mil Spec Type III Hard Coat Anodized Fabric/Material: 7075-T6 Aluminum Gun Make: AR Platform Gun Model: M16 M4 AR-15 Gun Type: Rifle Package Contents: Bravo Company MFG MK2 Receiver Extension What firearm models does the manufacturer say Bravo Company MFG MK2 Receiver Extension is compatible with? The manufacturer suggests that Bravo Company MFG MK2 Receiver Extension is compatible with AR-15 M4 M16Bravo Company MFG BCMMK2-RE: MK2 Receiver Extension Mil-Spec AR15/M16/M4 Black