Spur gear is one of the most common gears in actual production and use. It is a kind of gear classification method (Spur, Gear). According to the relative position of a gear tooth and axial (two weeks parallel) divided into planar gears and gear rotation gear; according to different working conditions can be divided into open and closed drive transmission; in accordance with the teeth or tooth profile shape is divided into straight teeth, helical, herringbone gear, or straight tooth and the curved tooth.

In order to make the right angle gear gear can rotate in the two direction, composed of tooth profile involute curved surface on both sides by the same shape, in the opposite direction, the names and symbols: addendum and dedendum circle, tooth and tooth thickness, tooth pitch, modulus of M, D, pitch, tooth top clearance.