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Typical components of a mechanical watch. Labeled diagram of a watch mainspring mechanism showing interconnected gears, the mainspring, balance wheel, winding pinion, escape wheel, and hands for hours, minutes, and seconds.
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Typical components of a mechanical watch.
Typical components of a mechanical watch.

A pinion is a machine part, specifically a gear with a small number of teeth designed to mesh with a larger wheel or rack. It is often the smaller of a pair of gear wheels. When a pinion meshes with a larger gear, it can either reduce speed and amplify torque if it's on the driving shaft, or increase speed and reduce torque if it's on the driven shaft.12

A rack and pinion system uses a toothed bar (the rack) that meshes with a small gear (the pinion). This mechanism can convert rotational motion into linear motion, or vice versa. For example, it's used in some car steering systems and on machine tools to move worktables.3

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  1. pinion
  2. gear
  3. rack and pinion

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