What machine did Leonardo da Vinci design to cut threads for screws with greater precision?

Leonardo da Vinci designed a thread-cutting machine for making more precise screw threads.

Screw threads were already known before Leonardo, but producing consistent threads by hand was difficult. In his engineering drawings, Leonardo explored machines that could guide a cutting tool along a workpiece and create a regular helical groove. Such mechanisms connected controlled rotation with controlled linear movement.

The idea belongs to Leonardo's wider work on machine tools. He designed and studied devices for shaping, drilling, grinding, and measuring materials, often seeking repeatable results rather than relying entirely on skilled handwork. Accurate screw threads were valuable for mechanical assemblies because matching threads allow parts to be tightened and released.

Leonardo's machine should not be confused with the modern engine lathe, which developed through later improvements in machine-tool technology. His drawings were influential as evidence of sophisticated Renaissance engineering, but they do not show that a complete production machine was built and widely used in his lifetime.