Worms and worm gears are gear sets that offer high gear reduction and torque multiplication with a small footprint. A worm drive is a cylindrical gear with a shallow spiral thread that engages the worm gear in a non-intersecting, perpendicular axes configuration.
Efficiency of a worm drive is determined by the lead angle and the number of threads in contact with the worm gear. A high lead angle on the drive reduces frictional losses and heat. A low lead angle reduces gear speed while proportionally increasing torque.
Friction is an issue with all worm sets; the worm gear cannot transfer motion back to the worm drive in most instances. Lubrication and ground teeth both contribute to the sets' overall silence while minimizing friction. Worm gear sets are usually produced in pairs due to their precision.