Radium Engineering valve for PCV (positive crankcase ventilation) systems. Do not mistake this for a simple one-way check valve. The PCV valve's internal plunger dynamically meters the appropriate amount of crankcase vent airflow based on current engine load. Proper PCV valves prevent the "vacuum leak" that a check valve would create at low loads. Also, in the event of a backfire, the PCV valve prevents combustible vapors from igniting in the crankcase. The PCV valves can be used on the outlet of any Radium Engineering Catch Can or any related part that uses -10AN ORB threads. 20-0683 SPECIFICATIONS Aluminum: 6061 Type-II Anodized Sealing O-rings: FKM and Silicone Inlet: 10AN ORB (7/8"-14 threads)Outlet: 5/16" SAE Quick Connect Male