The Holland's Primer Pocket Uniformer tool is designed to ensure that primer pockets are cut to the correct SAAMI depth specifications, cleaning out built up carbon residue from previous firings and squaring the bottom of the primer pocket with respect to the case head. This step is important as variations in the seating depth of the primer can change how the firing pin strikes the primer producing inconsistent ignition. This tool features a reversible cutting head for use on small and large primer pockets. Notes: To use, insert and turn tool to cut primer pocket base.Steel cutting head is held into the handle with a set screwCutting head is reversible for both large and small primer pockets