Though one may not think of gears to be versatile, gear couplings are very much considered to be a versatile coupling. A gear coupling is definitely a mechanical gadget made to transmit torque between two shafts that aren’t collinear. The coupling typically contains two flexible joints, one set to each shaft. These joints tend to be linked by a third shaft known as the spindle.
Each joint generally contains a 1:1 gear ratio internal/exterior gear pair. The tooth flanks and outer size of the exterior gear are crowned to allow for angular displacement between the two gears. Mechanically, the gears are equivalent to rotating splines with modified profiles. They are called gears because of the relatively huge size of the teeth. Equipment couplings are usually limited by angular misalignments of 4 to 5°.
Gear couplings ordinarily come in two variations, flanged sleeve and continuous sleeve. Flanged gear couplings consist of short sleeves encircled by a perpendicular flange. One sleeve is normally positioned on each shaft so the two flanges line up face to face. A number of screws or bolts in the flanges hold them together. Continuous sleeve gear couplings feature shaft ends coupled jointly and abutted against each other, which are then enveloped by a sleeve. Generally, these sleeves are made of metal, however they can also be manufactured from 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 flexible coupling. The solitary joint allows for minor misalignments such 
as installation mistakes and changes in shaft alignment because of operating conditions. These kinds of equipment couplings are usually limited by angular misalignments of 1/4 to 1/2°.