A single expansion joint is designed to permit angular rotation in any plane by the use of two pairs of hinges affixed to a common floating gimbal ring.
Unlike the hinged joint, which can absorb angular rotation in a single plane only, the gimbal joint can absorb angular rotation in any plane. The ability of the gimbal expansion joint to absorb angular rotation in any plane is most often applied by using two gimbal joints which act together to absorb movement. Gimbals, like hinges, are designed to transmit the pressure thrust and are used in pairs, or in conjunction with a hinged joint. A gimbal ring is either round or square. For round gimbals the torsional moment shall be considered and for square gimbals the instability due to the bending shall be considered.