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