The Ruger American Rifle Generation II stock features spacers that adjust the rifle's length of pull (LOP). The correct LOP enhances comfort and handling and improves accuracy by making shoulder placement and sight alignment quicker and more consistent. The rifle comes with a 13.75'' LOP spacer already installed. The spacers in this kit allow for additional LOP adjustments. The included spacers offer a 12.75'' or 13.25'' LOP when installed. To change spacers, loosen the recoil pad assembly and replace with the appropriate spacer. Only one spacer can be used at a time; spacers cannot be stacked for a longer LOP. Changing spacers is simple and quick with a 3/16'' hex wrench and a 7/16'' socket or wrench. A 1/8'' hex wrench or similar tool is needed to loosen the rear swivel stud (not included).