Abstract: A wrench has a handle with a jaw for gripping a workpiece. The jaw is formed of a first jaw member which moves transversely with respect to the handle and a second jaw member which is connected to the handle by an adjustment nut and extension to move relative to the first jaw member. An air motor delivers impact forces to a hammer which in turn transfers the impact forces to the first jaw member. The air motor is controlled by a valve secured to the handle. The surfaces of the jaw members may be exchanged to interface with specific workpieces.