A gear is a toothed part to transmit power or motion from a shaft to another or to change speed or direction. This elements are defined by several parameters, such as number of teeth, pitch, modulus, pressure angle, angle of action, etc. Exist a great variety of gears, depending of the tooth shape and function its possible make the following classification.

• Spur gear
• Helical gear
• Double helical gear
• Rack & Pinion
• Bevel gear
• Worm and worm gear
• Double Enveloping Worm Gear
• Face gear
• Hypoid gear