All parts of the chain are made of carbon steel or alloy steel and heat treated to improve strength, wear resistance and impact resistance. Roller chains can be made into single-row chains and multi-row chains. When transmitting large power, double-row chains or multi-row chains can be used. The bearing capacity of multi-row chain is proportional to the number of rows. However, due to the influence of precision, the load borne by side-by-side chain is not easy to be uniform, so the number of rows should not be too large.