Though one might not think of gears to be flexible, gear couplings are very much considered to be a versatile coupling. A gear coupling is normally a mechanical gadget designed to 
transmit torque between two shafts that aren’t collinear. The coupling typically includes two flexible joints, one set to each shaft. These joints are often linked by a third shaft known as the spindle.
Each joint generally includes a 1:1 equipment ratio internal/external gear set. The tooth flanks and outer diameter of the exterior gear are crowned to permit for angular displacement between the two gears. Mechanically, the gears are equivalent to rotating splines with altered profiles. They are known as gears because of the relatively huge size of the teeth. Equipment couplings are generally limited by angular misalignments of 4 to 5°.
Gear 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 certainly positioned on each shaft so the two flanges line up face to face. A series of screws or bolts in the flanges hold them jointly. Continuous sleeve gear couplings feature shaft ends coupled together and abutted against one another, which are then enveloped by a sleeve. Generally, these sleeves are constructed with metal, but they can also be made of Nylon.
Single joint gear couplings are accustomed to connect two nominally coaxial shafts. In this application the device is named a gear-type versatile, or flexible coupling. The single joint permits minor misalignments such as installation mistakes and adjustments in shaft alignment due to operating conditions. These kinds of equipment couplings are generally limited by angular misalignments of 1/4 to 1/2°.