This kit contains all the necessary parts to mount your Mil-Spec dimension stock assembly to your lower receiver. Receiver Extension - Mil-Spec, 6 position (machined from 7075T6) Receiver End Plate Lock Nut (Castle) M4 Carbine Action Spring Carbine Buffer Assembly (options for Std, H, H2, or H3) This kit is compatible with the plastic stocks from; BCMA(R), VLTOR, LMT, MagpulA(R) CTR-M, Stag Arms, Colt