The Edelbrock head bolt bushing kits allow you to use stock or aftermarket head bolts with Edelbrock or other aftermarket cylinder heads. They take the place of your head bolt washers and are hardened and chamfered. They are made of steel and come with a rich black zinc finish. The washer has an outside diameter of 0. 500 and an inside diameter of 0. 438. They are available as a set of 20.