Bravo Company's BCM Mil-Spec Carbine Stock Hardware Mounting Kit for AR-15's contains all the necessary parts to mount your Mil-Spec dimension stock assembly to your lower receiver- Receiver Extension (Mil-Spec, 6 position), Receiver End Plate, Castle Lock Nut, M4 action spring, carbine buffer assembly. This kit is compatible with the collapsible stocks from- BCM, VLTOR, LMT, Magpul CTR-M, Stag Arms, Colt and others.