Compatibility: Suitable for use on large trucks and trailers with air brakes with S cam design, and compatible with s-cam return spring. Function: This tool is designed to safely and easily install and remove return springs on commercial trucks and trailers with S Cam brake systems. Features: Unique design cups the return spring to prevent it from sliding off and causing injury. The slight bend at the end of the tool provides better fit and reduces slipping. Extra-long handle offers excellent stability. Quality: .