The arrangement of gears seen above is called a 
worm and worm wheel. The worm, which in this example is certainly brown in colour, just has one tooth nonetheless it is similar to a screw thread. The worm wheel, coloured yellow, is like a standard worm gear and worm wheel equipment wheel or spur equipment. The worm at all times drives the worm wheel round, it is never the opposite way circular as the system will lock and jam
