S&S Cylinder and Piston kits for 1936-'47 big twins feature premium quality U.S. made S&S cylinders and S&S forged 3-7/16" bore 74" pistons. The cylinders are cast from high strength engineering grade grey iron for superior wear resistance and heat dissipation, and are finished with durable gloss black high temp powder coat. These cylinders have been designed to look as much like OEM knuckle cylinder as possible.