The AGM Reservoir Piston Tool provides a quick and accurate method of measuring and setting shock reservoir piston depth during service. In addition, the AGM Reservoir Piston Tool can be used to monitor/prevent possible piston movement while bleeding air from your shock. Made in the U.S.A. from high-grade steel, it's heavy duty construction ensures proper function and long life. The AGM Reservoir Piston Tool works on all major brand name shock reservoirs and lengths.