Rolling is a metalworking process that involves passing metal stock between rollers to reduce the thickness and alter the cross-section. It was first developed in the late 1500s and today accounts for 90% of metal production. The main types are flat rolling, which produces sheet metal, and shapes rolling, which makes items like bars and rails. Sheets have a thickness under 6mm while plates are over 6mm thick. Rolling can be done hot or cold, with hot rolling used to refine castings and cold rolling providing better surface finish and tolerances.