Niresist Ring Set 964/993These CNC machined high nickel stainless steel rings provide a reliable interlocking seal between the cylinders and heads. Should the cylinder head lift slightly under combustion, the ring is a barrier against the combustion gas leaking out and damaging (melting) the machined sealing surfaces of the cylinder and head. Applicable to both high compression non turbo and elevated boost turbocharged engines, the concept dates back to the Porsche 935 race