What is the size of Chevy 305 cid SBC exhaust manifold stud nut?

The exhaust manifold stud nut for a Chevy 305 cubic inch small-block engine typically uses a 3/8-inch thread size. The nuts are usually 3/8-16, meaning they have a coarse thread pitch. The standard hex size for these nuts is generally 9/16 inch. Always verify the specific application, as variations can occur based on the year and model.