Spike's Tactical Rifle Buffer Tube Assembly, Includes Buffer, Buffer Tube, Buffer Spring, Castle Nut, End Plate, Fits AR-15 Rifles, Black SLA500R-K The Spike's Tactical carbine buffer assembly kit is just what you need to finish off your lower with quality components. This kit is perfect for those who either already have their own stock to use or just want to pick a different stock that isn't available from Spike's Tactical. Includes a 6 position mil-spec diameter buffer tube" ST-T2 heavy carbine buffer" carbine buffer spring" receiver end plate and castle nut.