Round Port header gaskets for Mark IV big block Chevrolet engines, built with a graphite core and steel outer layers for strength, heat resistance, and long-term torque retention. The graphite core conforms to minor flange irregularities, helps dissipate heat away from the cylinder head, and resists damage under extreme exhaust temperatures. A high-temperature silicone coating enhances sealing and prevents the gasket from imprinting or marking aluminum cylinder heads. Can be trimmed for modified port configurations. Designed for OE replacement as well as high-performance street, drag race, and oval-track applications.