Exchangeable square end mill heads have a square nose that creates a flat-bottomed groove with 90° inside corners. Also known as flat end-mill heads, they are used for counterboring, side and face milling, and milling square shoulders. These detachable heads have flutes that carry chips away from workpieces and a stem that connect to a compatible holder. They can be replaced with new heads of the same type or different types without removing the holder from the machine. They require fewer tool changes than solid tools when making different types of cuts on the same workpiece.