Abstract: A clamping jig releasably holds a workpiece of elongate cross section such as a radiator core. The jig includes an upright frame and a parallelogram-shaped horizontal articulated linkage having a pair of parallel side rails and a pair of end members pivotally connected to the ends of the side rails for movement about vertical axes. The side rails are spaced apart a distance greater than the width of a radiator core, and are moved by a pneumatic cylinder or other actuator so that the links pivot about their axes, and the side rails move closer together to clamp the radiator core between them. The clamping mechanism is operated by a foot pedal, for hands free operation. The vertical height of the parallelogram linkage may be readily adjusted, and hold-down elements are provided to exert a downward pressure on the radiator when it is held clamped between the side rails.