This is a UTG PRO AR-15 Ops Ready S4 Mil-spec Stock Kit molded from impact resistant high strength matte black polymer. It is complete with Mil-spec extension tube, buffer, buffer spring, receiver end plate, and castle nut. Its unique 4.28" length with 4 position adjustability provides comfortable length of pull and ease of shouldering firearm when wearing a load bearing vest or plate carrier system. It is built for heavy duty use with the tightest tolerance controls to provide the most secure fit and function.