All German Motorsports shock reservoir piston depth tool provides a quick and accurate method of measuring and setting the shock reservoir piston depth during service. The tool is an excellent way to monitor and prevent possible piston movement while bleeding air from your shock. Its heavy duty construction ensures proper function and long life. Works on all major reservoir brands and lengths that are threaded 1/4-20 such as King Shocks, Fox Shocks and Sway-A-Way.