The Ruger American Rifle Generation II stock incorporates spacers that adjust the stock's length-of-pull (LOP). The correct length-of-pull improves the rifle's comfort and feel and improve accuracy by making shoulder placement and sight acquisition faster and more consistent. The rifle ships with a 13.75'' length-of-pull spacer installed. The spacers in this kit allow additional adjustment to the rifle's LOP. The spacers included in the kit provide a 12.75" or 13.25" LOP when installed. Change spacers by loosening the recoil pad assembly and installing the appropriate spacer. Only one spacer can be utilized at a time; spacers cannot be stacked for extra-long LOP. Changing spacers is quick and easy using a 3/16'' hex wrench and 7/16'' socket or wrench. A 1/8'' hex wrench or similar tool is required to loosen the rear swivel stud (not included).