A gear is a rotating part having cut teeth, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage by changing the speed, torque, and direction of a power source.
These parts are in continuous rotation and must always mesh with another element. For that reason the accuracy and quality required in this kind of parts is extremely high.
Plastic gears can be found all over the car systems, including the latches, windows, wipers and air conditionings.