Though one might not think of gears to be flexible, gear couplings are very much considered to be a flexible coupling. A gear coupling is usually a mechanical device designed to transmit torque between two shafts that aren't collinear. The coupling typically consists of two flexible joints, one fixed to each shaft. These joints are often connected by a third shaft called the spindle.
Each joint generally contains a 1:1 gear ratio internal/exterior gear set. The tooth flanks and Cycloidal Reducer external diameter of the exterior 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 called gears because of the relatively huge size 
of the teeth. Equipment couplings are generally limited to 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 definitely placed on each shaft so the two flanges fall into line in person. A series of screws or bolts in the flanges hold them jointly. 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 from metal, however they may also be made of Nylon.
Single joint gear 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 allows for minimal misalignments such as for example installation mistakes and adjustments in shaft alignment because of operating circumstances. These kinds of gear couplings are usually limited to angular misalignments of 1/4 to 1/2°.