Involute gear

The involute profile is the most commonly used system for gearing today. An involute is a curve that is traced by a point on a taut cord unwinding from a circle, which is called a base circle. The involute is a form of spiral, the curvature of which becomes straighter as it is drawn from a base circle and becomes a straight line at infinity. An involute drawn from a small base circle is more curved than one drawn from a larger base circle.

The involute profile can be generated using a hobbing machine with a rack form, which has a pressure angle of 14.5 degrees or 20 degrees.

Small pinions have a modified form call addendum modification.