worm gear and worm wheel

The arrangement of gears seen above is named a worm and worm wheel. The worm, which in this example is brown in colour, just has one tooth nonetheless it is like a screw thread. The worm wheel, coloured worm gear and worm wheel yellow, is like a standard gear wheel or spur gear. The worm often drives the worm wheel round, it is never the contrary way round as the system tends to lock and jam