The BOP Pontiac steel core Neoprene (rubber) valve cover gaskets are the ultimate in sealing and reusability. The steel core maintains the shape of the gasket in-plane for improved sealing especially in vacuum pump applications. Gaskets will not get sucked into the valve train area or push out. At 3/16 inches thickness (.187") they also aid in clearance issues with roller valve trains, especially when doubled up.