Machine component consisting of a toothed wheel attached to a rotating shaft. Gears operate in pairs, the teeth of one engaging the teeth of a second, to transmit and modify rotary motion and torque. To transmit motion smoothly, the contacting surfaces of gear teeth must be carefully shaped to a specific profile. The smaller of a gear pair is often known as the pinion. If the pinion is on the driving shaft, the pair acts to reduce speed and to amplify torque; if the pinion is on the driven shaft, the pair acts to increase speed and reduce torque.

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