What is the term for the insert found between coupling halves?

The term for the insert found between coupling halves is referred to as a "spider." In mechanical coupling systems, the spider acts as a flexible connector that cushions and absorbs shock between the two halves (or hubs) of a coupling. This flexibility is crucial as it allows for the accommodation of misalignment and helps to reduce vibrations that could otherwise lead to premature wear of the machinery components.

A spider is typically made from a rubber or polymer material, which provides the necessary flexibility while maintaining strong torque transfer capabilities. This design helps to ensure a smooth connection between the driving and driven shafts, enhancing operational efficiency and longevity.

The other terms listed do not accurately describe this component. "Center" could refer to the middle part of a coupling but does not specify the insert role. "Elastomer" describes a class of materials used, including those which may form a spider, but does not identify the component itself. "Joint" generally pertains to the connection point in mechanical systems, which is broader and not specific to the insert between coupling halves.