An extension is attachable to the driving shaft of a reciprocating blade tool such as a saber saw. The extension is attached to the drive shaft and the blade is attached to the end of the extension. The extension places the blade at a position spaced laterally and longitudinally from the nominal point of attachment of the blade to the driving shaft, the lateral spacing placing the new blade position approximately at the lateral outside edge of the tool housing, thereby permitting flush cuts. The extension can be formed of an integral strip or sheet having a proximal leg, an intermediate section and a distal leg, joined at equal and opposite obtuse angles. The angles are reinforced by two or more webs bent from the plane of the legs and attached, for example by welding, to the intermediate section.