Edelbrock part #7241 Exhaust Gaskets are designed for 1958-1965 Chevy 348/409 "W Series" V8 engines. These Exhaust Gaskets are made of EnCore HTX-900; a high-density non-asbestos fiber/metal core composite material consisting of two graphite coated, heat resistant fiber blended sheets that are mechanically and chemically fused to an expanded steel core. The finished product provides high heat resistance, excellent load retention and unmatched sealing performance on exhaust manifold and header applications. A 50% recovery rate allows for gasket expansion in the event your header loses the proper header bolt torque. Gaskets future a 1.813"x 1.75" port size.