A pinion is the smallest gear in a gear drive train. Many people believe that the gear directly on a motor shaft is the pinion. This is not true. This misconception may come from the fact that in many cases such as remote controlled toys like model cars and model railways the drive gear is also the smallest gear.

Commonly used to describe the smaller gear that drives in 90 degree angular towards a crown gear in a differential drive.

Other meanings

• See Pinion (feather)
• Pinion (verb); If you pinion someone, you prevent them from moving or escaping, especially by holding or tying their arms. ...pinioned by the press of men around them, they were unable to move.

Gears

Pignon (mécanique) | Antriebsritzel