worm gear and worm wheel

The worm gear and worm wheel arrangement of gears seen above is named a worm and worm wheel. The worm, which in this example is usually brown in colour, just has one tooth nonetheless it is like a screw thread. The worm wheel, coloured yellowish, is like a standard equipment wheel or spur gear. The worm generally drives the worm wheel round, it is never the opposite way round as the system will lock and jam