Double-end square end mills have cutting edges on both ends and can accomplish more milling tasks than single-end end mills before they need to be replaced. Flip the end mill over when the cutting edges on one end wear down to expose the fresh cutting edges on the other end. Square end mills have a square nose at both ends and are rotated against a piece of stock to create flat-bottomed grooves with 90° inside corners. They are used for counterboring, side and face milling, and milling square shoulders. Double-end square end mills are used on CNC or manual milling machines.