Don't allow small headers to exhaust your engines power! JEGS bolt-on SB-Chevy to Stahl header adapter plates allow you to use big tube headers on both GM and aftermarket SB-Chevy cylinder heads with a standard exhaust bolt pattern. Features 5/8'' thick CNC machined 6061 T-6 Billet aluminum plates - No need for thread inserts. Port openings are left small (1.1'' x 1.1'') to allow for port matching. We recommend 555-210053 gasket set (not included) for the adapter plate to cylinder head. Made in the USA.