For 1955 1956 1957 Black Coated Shorty Hugger Headers SBC Corvette Bel Air For 1955 1956 1957 Black Coated Shorty Hugger Headers SBC Corvette Bel Air The collector opening is 2 1/2" Heavy duty quality parts. 18 gauge tubes and 3/8" flanges. Work with both angle plugs and straight plug All the necessary install hardware is included, like the bolts, gaskets, and collectors