Involute gear

The involute gear profile, originally designed by Leonhard Euler, is the most commonly used system for gearing today, with cycloidal gearing still used for some specialties such as clocks. In an involute gear, the profiles of the teeth are involutes of a circle. (The involute of a circle is the spiraling curve traced by the end of an imaginary taut string unwinding itself from that stationary circle called the base circle.)