Abstract: Power tools of the type under consideration include hammer drills, for example, which are electric or battery powered and includes two modes of operation: a rotation mode and a rotation-hammer mode. A manually operable selector lever enables the hammer drill to be selectively operated in one of the two modes by disengaging and engaging a hammer mechanism. In rotation-hammer mode, the drive shaft of the hammer drill rotates a tool element about a rotational axis and oscillates the tool element along a rotational axis. An attachment mountable within the chuck of a hammer drill prevents a tool element from rotating when the hammer drill is operating in rotation-hammer mode. The hammer drill attachment transfers hammer action, but not rotation, to the tool element. The hammer drill attachment enables dual function power tools to be operated in a hammer only mode to perform a function, for example, chiseling.