Performance Header Gaskets Fits 1965-1990 Chevrolet 396-454 Big Block Round Ports, 1.85 Inch x 1.90 Inch Mr GasketMr. Gasket Performance Header Gaskets are manufactured from a heavy duty high temperature material, . 062 inch thick, consisting of an acrylic binder system to resist high temperature. Provides excellent sealing and durability with maximum torque retention to eliminate Gasket failure. While precision die cut for an excellent fit, it can be trimmed if necessary for modified port applications. For original equipment replacement, higher performance