LBE Unlimited Mil-Spec Buffer Tube Kit , Contains Buffer Tube, Castle Nut, Lock Plate, 6 Position, Fits AR-15, Black MILBUFKT This LBE Buffer Tube Kit includes a six position mil-spec diameter buffer tube" carbine length recoil spring" standard carbine recoil buffer" receiver end plate" and castle nut. LBE Unlimited is a leading producer of US Made gun parts and accessories.