Commonly used steel manufacturing gears are hardened and tempered steel, hardened steel, carburized steel hardening and nitriding steel. Slightly lower than the strength of the cast steel forging steel, often used for large size gear; Poor mechanical properties of gray cast iron and can be used for light load of open gear transmission; Nodular cast iron can partly replace steel manufacture gear; Plastic gear is used for light load and more requirements of low noise, and its gear pairs, the thermal conductivity is commonly used in steel gears.