Parallel misalignment is the offset of two mating shaft centerlines although the centerlines remain parallel to each other. Angular misalignment is two shaft centerlines intersecting at some angle other than zero degrees. End float is the relative displacement of one shaft end with respect to the other.

A single-flex coupling accepts angular misalignment only. That means it acts as a hinge or a pivot and cannot accept parallel misalignment. A double-flex coupling accept both angular and parallel misalignment. It may be visualized as two single-flex couplings with a short spacer or distance between the pivots. Depending on their design, both single-flex types may or may not accept end float. A rigid coupling, as its name implies, is merely a set of rigid flanges mounted on a shaft. It cannot compensate for or permit any misalignment.

A single-flex coupling accepts angular misalignment only. That means it acts as a hinge or a pivot and cannot accept parallel misalignment. A double-flex coupling accept both angular and parallel misalignment. It may be visualized as two single-flex couplings with a short spacer or distance between the pivots. Depending on their design, both single-flex types may or may not accept end float. A rigid coupling, as its name implies, is merely a set of rigid flanges mounted on a shaft. It cannot compensate for or permit any misalignment.