Includes air regulator, 0 - 100 PSI pressure gauge, plugs for water and oil cooled oil pumps, gasket and needed hardware.Only fits Feuling™ oil pumps, will not work with factory Harley-Davidson oil pumps.The spring tension can be adjusted to achieve the desired pop off PSI.Allows the engine builder to know what PSI the relief valve opens.Feuling™ oil pump pressure test tool for Feuling™ M8 oil pumps.Made in the U.S.A..