Though one might not think of gears as being flexible, gear couplings are extremely much regarded as a versatile coupling. A gear coupling is usually a mechanical device made to transmit torque between two shafts that aren’t collinear. The coupling typically consists of two flexible joints, one set to each shaft. These joints are often linked by a third shaft called the spindle.
Each joint generally consists of a 1:1 equipment ratio internal/external gear pair. The tooth flanks and external diameter of the exterior equipment are crowned to permit for 
angular displacement between the two gears. Mechanically, the gears are equal to rotating splines with altered profiles. They are known as gears because of the relatively large size of one’s teeth. Gear couplings are usually limited by angular misalignments of 4 to 5°.
Gear couplings ordinarily can be found in two variations, flanged sleeve and continuous sleeve. Flanged equipment couplings consist of short sleeves encircled by a perpendicular flange. One sleeve is normally placed on each shaft so the two flanges fall into line face to face. A number of screws or bolts in the flanges keep them together. Continuous sleeve equipment couplings feature shaft ends coupled collectively and abutted against each other, which are after that enveloped by a sleeve. Generally, these sleeves are made of metal, however they may also be made of Nylon.
Single joint equipment couplings are used to connect two nominally coaxial shafts. In this application these devices is called a gear-type flexible, or versatile coupling. The single joint permits small misalignments such as installation mistakes and adjustments in shaft alignment due to operating circumstances. These types of equipment couplings are usually limited by angular misalignments of 1/4 to 1/2°.