Abstract: A tool is provided for drilling a hole in a construction material precisely concentric to a nearly inaccessible reference aperture situated opposite the side of the construction material from which the hole must be cut. A typical application is in cutting a sprinkler head receiving hole concentric with the open end of a downwardly directed drop of a sprinkler distribution system. The tool includes an elongated rod which carries a sliding guide member constrained between a stop positioned at one end of the rod and a compression spring urging the guide member toward the stop. Intermediate the length of the rod, there is provided a hole saw retaining shoulder against which a conventional hole saw of the desired diameter cut to receive a sprinkler head may be affixed with its teeth directed toward the rod first end.