Helical-flute thread mills have spiral flutes that distribute the chip load as the thread mill removes material to cut threads into an existing hole or onto the external surface of a part. They provide a smoother cut than straight-flute or single-profile thread mills and are used to create threads on tough or thin-walled materials. Helical-flute thread mills can create internal threads of the same pitch in a range of hole diameters, eliminating the need to change tools when threading multiple holes of different sizes. Thread mills are only usable in CNC machines that have helical interpolation capability.