The arrangement of gears seen above is worm gear and worm wheel 
called a worm and worm wheel. The worm, which in this example is definitely brown in colour, only has one tooth nonetheless it is similar to a screw thread. The worm wheel, coloured yellowish, is like a standard equipment wheel or spur gear. The worm constantly drives the worm wheel round, it is never the contrary way circular as the system tends to lock and jam
