The arrangement of gears seen above is named a worm and worm wheel. The worm, which in this example is usually brown in colour, only has one tooth but it is similar to a screw thread. The worm wheel, coloured worm gear and worm wheel yellow-colored, is like a normal gear wheel or spur equipment. The worm generally drives the worm wheel circular, it is never the contrary way round as the system will lock and jam