How did change gears allow Maudslay's lathe to cut threads with different pitches?

Henry Maudslay’s screw-cutting engine lathe, developed in 1797, revolutionized precision manufacturing by utilizing a lead screw to drive the tool carriage at a constant speed, ensuring the production of accurate threads.1

To achieve different thread pitches, Maudslay equipped his lathe with a set of 28 change gears by 1800. These gears allowed the operator to control the ratio between the speed of the lead screw and the speed of the spindle. By adjusting this gear ratio, the lathe could precisely regulate how far the cutting tool advanced relative to the rotation of the workpiece, thereby determining the specific pitch of the thread being cut.1