Gear couplings are common mechanical part used to transmit torque in gear reducer. Divided into two parts, the driving shaft and driven shaft. The general power machine is mostly connected with the working machine by means of it. Gear couplings are often used to transfer torque to gear reducers. According to the structure can be divided into full gear coupling and half gear coupling. Simple to install, but heavy and costly. Often used in medium and low speed heavy machinery. The material is usually 45# steel or ZG45 cast steel. The greater the drum degree of the tooth length of the internal and external teeth, the greater the angular displacement, up to 6°, the general use of 1° ~ 1.5° recommended, and the old gear couplings only allows 0.5°; In terms of bending strength and load capacity, the transmission torque of drum-tooth coupling can be increased by 15-20% under the same working conditions. Drum type china gear couplings has the advantages of large transmission capacity, large angular displacement, smooth transmission, high efficiency, long life and so on. Therefore, it gradually replaces straight tooth coupling, and is widely used in metallurgical machinery, heavy, mining machinery, lifting, transportation machinery and other transmission.Large torque drum gear coupling has good impact bearing performance. However, the tooth surface contact stress and root bending fatigue strength are highly required. If we take special structure, special material, special process, then the coupling can meet the requirements of large diameter pipe rolling machine.