Though one might not think about gears as being flexible, gear couplings are very much considered to be a flexible coupling. A equipment coupling can be a mechanical device made to transmit torque between two shafts that are not collinear. The coupling typically includes two versatile joints, one fixed to each shaft. These joints are often linked by a third shaft known as the spindle.
Each joint generally consists of a 1:1 equipment ratio internal/exterior gear pair. The tooth flanks and external size of the external equipment are crowned to allow for angular displacement between your two gears. Mechanically, the gears are equal to rotating splines with modified profiles. They are known as gears because of the relatively large size of the teeth. Gear couplings are usually limited to angular misalignments 
of 4 to 5°.
Equipment couplings ordinarily can be found in two variations, flanged sleeve and continuous sleeve. Flanged gear couplings contain short sleeves encircled by a perpendicular flange. One sleeve is usually positioned on each shaft so the two flanges fall into line face to face. A number of screws or bolts in the flanges keep them collectively. Continuous sleeve gear couplings feature shaft ends coupled collectively and abutted against one another, which are after that enveloped by a sleeve. Generally, these sleeves are made from metal, but they can also be made of Nylon.
Single joint gear couplings are accustomed to connect two nominally coaxial shafts. In this application these devices is called a gear-type flexible, or versatile coupling. The single joint allows for small misalignments such as installation errors and changes in shaft alignment because of operating conditions. These kinds of equipment couplings are generally limited to angular misalignments of 1/4 to 1/2°.