Abstract: The invention discloses a three-piece clamping device especially adapted for clamping together an inner packing box and an outer packing box or clamping together the packing boxes. The clamping device comprises a pair of rectangular retaining members similar in construction and a retaining wedge member with a knob or wing. According to one preferred embodiment, each retaining member has a saucer-shaped flat-bottomed barrel portion formed by a drawing operation, and a flange portion extending outwardly from the periphery of the open end of the barrel portion. An elongated-hexagon-shaped slot is formed through the flat bottom of the barrel portion, a projection is extended outwardly from the outer bottom surface and a recess is formed in the outer bottom surface of the barrel portion.