Conveyor sprockets (mill sprockets, engineering class sprockets, engineered sprockets) are used in conjunction with conveyor chains or conveyor belts. They are toothed gears or profiled wheels that mesh with a conveyor chain or belt to transmit rotary motion. Single, double, triple, quadruple and quintuple conveyor sprockets are commonly available. Dimensional specifications for conveyor sprockets include number of teeth, bore diameter, hub diameter, outside diameter, length-through bore and weight. Material selection is dependent on power-transmission and speed, environmental factors such as operating temperature and exposure to corrosive elements, and considerations such as noise generation. All-plastic hubs are relatively quiet, but suitable only for light to medium duty applications. Conveyor sprockets with hubs made of steel, stainless steel, or hardened steel are also available.