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