In mechanical engineering, it is accepted to call a small gear wheel a gear, and a large-a wheel. However, often all gears are called gears. The origin of the word is unknown. According to one version of the earlier division of the circle into six sectors was the most convenient. Hence the name. But there are other versions. Gears are usually used in pairs with different numbers of teeth to convert torque and the number of revolutions of shafts at the inlet and outlet. The wheel to which the torque is supplied from the outside is called the master, and the wheel from which the moment is removed — the slave.