Abstract: An improved hammer drill adapter, that is to be inserted into the variable-diameter, chuck end of a hammer drill for driving forward any one of a plurality of different types of sheet metal cleats to join the opposing ends of two sheet metal, duct sections, includes: (a) an elongated shaft having a drive end and a working end and a centerline between said ends, (b) the drive end configured to be releasably held in the hammer drill's chuck, (c) the working end having an elongated flat, front face that has top and bottom surfaces, two ends and with the front face oriented so that a perpendicular to the front face is parallel to the shaft's centerline, (d) the front face has an elongated cavity and a front face channel that are oriented approximately perpendicular to each other, and (e) wherein this cavity is configured to accommodate within it the end of a flat drive cleat, and the cavity and front face channel together are configured to accommodate within them the end of a standing drive cleat.