This kit contains all the necessary parts to mount a Mil-Spec dimension stock assembly to your lower receiver. Kit Includes the following:
 
6 position Mil-Spec diameter Receiver Extension (machined from 7075-T6 aluminum and Type III hardcoat anodized) 
Receiver End Plate 
Steel M4 Castle Nut, heat treated with phosphate finish 
Carbine Action Spring 
Standard Carbine Buffer