Mr. Gasket Copper Seal Header Gaskets are made from dead soft solid Copper .043 inch thick. This gasket incorporates .051 inch embossment around each port to seal irregular surfaces, total gasket thickness is .094 inch. Provides excellent sealing and durability. Conforms to and seals minor surface irregularities. designed for high-performance street, drag race, oval track and turbocharged (extreme heat) applications.