Mr. Gasket Copper Seal exhaust gaskets are made from inDead Soft in solid Copper .043 in thick. This gasket incorporates .051 in embossment around each port to seal irregular surfaces, total gasket thickness is .094 in. Provides excellent sealing and durability. Conforms to and seals minor surface irregularities. designed for high-performance street, drag race, oval track and turbo-charged (extreme heat) applications. Fits Small Block Chevy 1955-91 262-400 CID