GM-46143-A is used to pressure test cooling systems and surge tank caps for leaks. Threads on to the surge tank to allow pressure testing of the entire cooling system. It has a center core with O-rings that seal off the tank vent port so the system will pressurize and the test can be run correctly. Threads on to the surge tank cap to test it for any seal leaks. Both adapters are used with the GM-24460-A Pressure Tester Pump.