Door Hinges 3" x 3" x 2.0 mm Ball Bearing Stainless Metal Satin Stainless Finish HD5001SS ( Herks)A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation, with all other translations or rotations prevented; thus a hinge has one degree of freedom.