A worm and wheel are generally found in a transmission with a high gear ratio. the worm gear has a screw like form and is generally produced out of steel, this increases the life of the worm gear and causes the wheel to wear rather than having equal wear. meaning the wheel will need replacing rather than a pair of gears needing replacing. the worm wheel is usually made out of brass or a bronze material but can be made out of steel also, this has a form similar to a helical gear. in worm and wheel gears each 360 degree rotation of the worm shaft will move the wheel one tooth.