Receiver Extension - Mil-Spec, 6 position (machined from 7075T6) Receiver End Plate Lock Nut (Castle) M4 Action Spring, Carbine Buffer Assembly, Carbine Std (options for H, H2) This kit contains all the necessary parts to mount your Mil-Spec dimension stock assembly to your lower receiver.table.productattributes, .productattributes td { border-bottom: 1px solid #ddd; border-collapse: collapse; padding: 2px; text-align: left; }