Threading tool

With the aim to thread a screw, Leonardo devised a drilled block where a cutting tool and a guide bearing are embedded. Before performing this operation, the screw thread has to be cut by hand. The taps were designed as a three-piece tool with cross-sectional areas of increasing ratios. The three taps forming a wye, two of them act in turn as handles for driving the third.
Codex Atlanticus, sheet 1025 v.