A worm gear is a helical thread formed on a shaft with the same tooth profile as a spur gear (the more conventional form, perhaps, in the form of a wheel). If a worm gear is mated with a spur gear and the shaft with the worm on rotated it will transfer motion to the spur gear which will rotate in turn. Think of the individual teeth of the spur gear being pushed along the worm (until the curvature of the wheel makes them fall off, by which time one rising from the other side will have joined in instead) It is a curious property of a worm-and-wheel drive that the arrangement is reasonably efficient if the worm is rotating and driving the wheel, but hopelessly poor if you attempt to rotate the wheel. Friction makes it very hard to drive the worm from the wheel. Above we briefly introduced about worm gear.If you would like to know more then freely follow us www.ttmotor.com Nice Day !