Abstract: This clamping device provides opposed banks of clamping units attached to an associated reaction beam above a work table, for clamping workpiece plates to the table during seam welding. Each clamping unit includes an upright clamping member, having an inclined finger engageable with a workpiece plate, and each member is connected to its reaction beam by a pair of transverse link members: the clamping member, link members and the reaction beam cooperate to provide a four-bar linkage. Downward pressure is applied to the clamping members by an inflatable flexible hose positioned between the lower link member of each unit and an associated reaction beam and the clamping members are upwardly biased by individual return springs extending between the upper link member and the reaction beam.