Below is a list of Worm Gears manufacturers from Chicago, Illinois. Worm gears are the combination of a simple spur gear and a worm. A worm is a threaded metal rod that looks like a screw. Worms distinguish themselves from screws in that they are only machined in the middle; the threads do not begin or end at either end of the rod. The spur gear comes into contact with the worm at its threaded middle section. If the spur turns, it causes the worm to rotate. If the worm rotates, it causes the spur to turn.