Gears are used as elements of gear trains for transmission and transformation of a motion from a driving shaft to a driven shaft. A large number of gears are used in the automotive industry (Figure 2.1). It is commonly understood that a gear is a machine element with gear teeth. Usually, but not necessarily, the gears are round. 1 There is a large variety of gear forms, as well tooth forms, in the lengthwise direction. Gear teeth are also available in a wide variety of profiles.