Copper Seal Header Gaskets Port Size 1.45 x 1.48 Fits 1955-1991 Chevrolet 262-400 Gen I Small Block Rectangular Ports Mr GasketMr. Gasket Copper Seal Header Gaskets are a high quality copper Gasket that performs extremely well and are reusable. We recommend this in all racing and high performance applications. They are for stock heads unless indicated, and work well in high heat and turbocharged applications. Manufactured from Dead Soft (solid) . 043 Inch thick copper material . 051 Inch embossment around each exhaust port to seal irregular surfaces. Total Gasket thickness .