Fits 1955-1991 Chevrolet 262-400 Gen I Small Block. Rectangular Ports;Manufactured from “Dead Soft” (solid) .043" thick copper material; .051" embossment around each exhaust port to seal irregular surfaces. Total gasket thickness .094"; Provides excellent sealing and durability; Conforms to and seals minor surface irregularities; For high performance street, drag race, oval track and turbocharged (extreme heat) applications;