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