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