Abstract: This invention relates to a "T" shaped doweling jig and an attachable convertible clamp device for holding a work part. The doweling jig is comprised of a drill bit guide hole member and a base plate. The drill bit guide hole member is provided with at least one defined drill bit guide hole which is interchangeable with other guide hole members and provides a range of defined drill bit diameter guide holes. The base is provided with at least one alignment port hole, cut-outs and alignment indicies that correspond with said guide holes, and provides for the correct positioning and clamping of the doweling jig over the work part, and the subsequent passing of the drill bit through a guide hole in one direction to drill the first work part, and consecutively to pass the drill bit through the same guide hole in the opposite direction to drill a mirror image hole in a second work part.