A jaw coupling is a kind of general purpose power transmission coupling that also can be used in motion control (servo) applications. It really is designed to transmit torque (by connecting two shafts) while damping program vibrations and accommodating misalignment, which protects other components from damage.
Jaw Couplings are one of the first and still most widely used elastomer couplings in the globe because of their inherent simplicity. Two identical hubs with 3 encounter lugs are linked through a star shaped element, sometimes known as an insert or spider. The 3 piece style makes them easy to work with and popular on applications such as pumps, fans, blowers and compressors.
Jaw Couplings require no lubrication and provide high dependability for light to moderate duty applications with good alignment of equipment no requirement of torsional dampening.
In normal operating conditions there is absolutely no metal to metallic contact therefore the life of the hubs is virtually indefinite. Nevertheless, in a catastrophic failure of the element the load would still be carried by the hubs providing a degree of failure safety. 
Jaw couplings are resistant to essential oil, dirt, wetness and grease.
Specific element materials are available to achieve optimum performance for the working conditions.
The standard element materials is NBR (N)-‘Synthetic Rubber’. It is highly flexible, oil resistant and the torsionally softest of the element options. It has a temperatures operating range suitable for most industrial applications and allows for up to 1 1 degree misalignment capability of the linked shafts. NBR is the most economically priced option.