The worm gear and worm wheel arrangement of gears seen above is called a worm and worm wheel. The worm, which in this example can be brown in colour, only has one tooth but it is like a screw thread. The worm wheel, coloured yellow-colored, is like a standard gear wheel or spur equipment. The worm at all times drives the worm wheel round, it is never the contrary way round as the system tends to lock and jam