Spur gears, or straight-cut gears, are the simplest and the most widely used gears that can achieve high accuracy with relatively easy production processes. The gear teeth are cut on the periphery and are parallel to the axis of the gear. Though the teeth are not straight-sided (but usually of special form to achieve a constant drive ratio, mainly involute but less commonly cycloidal), the edge of each tooth is straight and aligned parallel to the axis of rotation.
Spur gears are used to transmit power and motion in the same plane or when the driving and driven shafts are parallel to each other. They have the characteristic of having no load in the axial direction (thrust load). The larger of the meshing pair is called the gear and smaller is called the pinion.