A tool for repositioning a plunger is formed from a pair of concentric and relatively rotatable shafts. The inner and tubular outer shafts respectively support enlarged forward and rear head elements. The shafts are relatively rotatable between a first position, in which the cross-sectional profiles of the head elements are aligned, and a second position, in which the cross-sectional profiles of the head elements are in skewed opposition. A ball detent mechanism at the interface between the forward and rear head elements permits accurate location of the first and second positions. The tool is used with a tubular collar element having a stem section and an enlarged flange section, and a disk-shaped platform element having a centrally disposed and internally threaded opening. The threaded opening in the platform element receives the externally threaded outer shaft of the tool.