Worm gears are usually used when large quickness reductions are needed. The decrease ratio depends upon the number of starts of the worm and amount of tooth on the worm equipment. But worm gears have sliding contact which is peaceful but will produce heat and also have relatively low transmission performance.
As for the materials for production, in general, worm is made from hard metal as the worm gear is manufactured out of relatively soft metal such as aluminum bronze. That is because the number of tooth on the worm equipment is relatively high compared to worm using its number of starts being usually 1 to 4, by reducing the worm gear hardness, the friction on the worm teeth is reduced. Another feature of worm manufacturing may be the need of specific machine for gear trimming and tooth 
grinding of worms. The worm equipment, however, may be made with the hobbing machine used for spur gears. But because of the various tooth shape, it is not possible to cut many gears simultaneously by stacking the gear blanks as can be carried out with spur gears.
The applications for worm gears include equipment boxes, fishing pole reels, guitar string tuning pegs, and in which a delicate speed adjustment by utilizing a big speed reduction is needed. When you can rotate the worm gear by worm, it is normally extremely hard to rotate worm by using the worm gear. That is called the personal locking feature. The self locking feature cannot worm wheel china always be assured and another method is recommended for accurate positive reverse prevention.