Stanley Proto FM-31.12X13 Facom Tappet Satin Open-End Wrench - 12 x 13 mm Satin finish provides corrosion resistance and a slip resistant grip. Used to tighten collars, lock nut rings and help seal packing nuts on hydraulic cylinders. Ultra thin profile for use in close quarters. Openings designed to cover tappets, screws and lock nuts with excessive overhang which helps improve access. For use in low torque applications.