Hinges are devices that permit bending at the joints of rigid elements (plate 14B). The most common type of hinge is a pair of metal plates with interlocking fingers wrapped around a pin (plate 13A). These hinges facilitate rotation of one or both plates around the axis of the pin. Hinges come in a wide variety of sizes beyond the common door and window hinges (plate 14A-D). Certain number of our joints, for instance in the hand joints (plate 15B), are hinge joints (plate 13A). Like mechanical hinges, they provide for bending only in single plane.
