Abstract: A workpiece holding assembly for use on a chuck includes a chuck jaw and an adjustable self-centering workpiece holder. The chuck jaw has an elongated body with opposite ends, a groove defined in one end of the body, and a pair of arcuate recesses formed in the one body end on opposite sides of the groove. The workpiece holder includes a shaft portion and a base portion attached about a midsection of the shaft portion such that the holder has an integral, one-piece construction. The shaft portion is of generally cylindrical shape adapted to extend into the arcuate recesses of the one chuck jaw body end. The base portion is of greater than semi-circular shape and adapted to extend into the groove of the one chuck jaw body end. The base portion also has a generally semi-circular closed slot defined therethrough adapted to receive at least one fastener therethrough being fastenable to the one chuck jaw body for releasably clamping the base portion in the groove.