The Griffin Armament Stock Mount Kit includes the heavy Griffin AR-SOB A2 length buffer, Griffin AR-10/"GA A2" 7075-T6 Maritime Receiver Extension, (Similar to industry A5 Length), corresponding AR-15 / M16A2 rifle length 17-7 wire spring, QD Contour Connect End Plate, and castle nut. All these parts will complete the back end of your lower receiver. This kit is applicable to AR-15 pattern firearms in 5.56 NATO and similar calibers, and is compatible with Mil-Spec dimensioned butt-stocks. This kit should not be used in conjunction with a standard "CAR" length buffer. The use of a shortened buffer in this special kit will allow the bolt carrier key to collide with the receiver and can damage the rifle.