What machine did Leonardo da Vinci design to cut a continuous screw thread in metal?

Leonardo da Vinci designed a thread-cutting machine for producing a continuous screw thread in metal.

Leonardo’s mechanical notebooks contain designs for machines that could guide a cutting tool along a rotating workpiece. By coordinating the workpiece’s rotation with the cutter’s movement, the machine could create a regular helical thread. Such controlled screw production was valuable because accurate screws were difficult to make by hand.

The machine belongs to Leonardo’s wider study of workshop technology, which included gears, lathes, presses, and systems for converting rotary motion into linear motion. His drawings show mechanical principles rather than proof that every proposed machine was constructed.

This invention is sometimes confused with Leonardo’s designs for a screw press. A screw press uses a threaded shaft to apply force, while a thread-cutting machine makes the thread itself. It is also different from the later industrial screw-cutting lathe, which used increasingly precise lead screws and machine-tool practices.