Double-end cobalt ball end mills have a rounded nose on both their ends and can accomplish more milling tasks than single-end end mills before they need to be replaced. When the cutting edges on one nose wear down, the end mill can be flipped over to expose the fresh cutting edges on the other nose. Cobalt end mills can be used at higher speeds and are harder and more wear-resistant than high-speed steel end mills. Also known as ball-nose end mills, ball end mills are rotated against a workpiece to make round-bottomed slots and pockets or mill complex shapes without sharp corners.