This is the CMMG AR-15 Carbine Receiver Extension Kit. Complete your AR’s buffer system with this all-inclusive kit from CMMG! Constructed from aluminum and featuring a hard coat anodized finish, you’ll never have to worry about its durability. The only thing you’ll need to add is your favorite stock or brace, as all of the following is included: Carbine Buffer Tube Receiver End Plate Castle Nut Action Spring Buffer Whether you’re building a home defense or competition rifle, you can easily complete it with this kit!