Couplings permit rotary transmission of motion, power and torque from a driving to a driven component. For example, a motor to a shaft or gearbox.

There are numerous variants and some of the more common types include, jaw coupling, chain coupling, fluid coupling, tyre coupling and rigid sleeve coupling.

Selection criteria to be considered are, speed, torque, power, application, environment, space availability, alignment requirements, damping requirements and service factor.

Accurate and clean setup is critical for a long service life and mating parts must be machined to precise form, surface finish and size.

Typical coupling mounting/drive arrangements include parallel drive key, pinned connection or taper bush.

Coupling failures can occur if, the coupling is underrated for the task, the coupling selected is simply unsuitable for the application, misaligned coupling halves, machine overload, temperature extremes, corrosion and of course general wear and tear.

Coupling spider inserts are used in jaw couplings and are often manufactured from NBR (nitrile rubber), Urethane or Hytrel. These material properties are different and therefore have varying torque capacities and damping characteristics and care should be taken during initial design or later selection of replacement inserts. The design geometry of an insert can change from one coupling type to the next or from one manufacturer to the next and are therefore not always interchangeable.

A typical example of a jaw coupling with spider insert is shown below.