a dual - function electrical hand drill includes an electrical motor to which a driving shaft is coupled via a speed reduction gear train . a chuck is releasably secured to the driving shaft to be rotatable therewith . a setting ring is provided to change the rotation speed and thus the output torque by applying force to the speed reduction gear train via the compression of a helical spring . a serrated member , secured to the driving shaft , is provided to be movable between a disabled position and an enabled position in which enabled position , the serrated member engages a counterpart serration and is biased by a spring to allow the chuck and the bit secured thereto to move to and fro by the sliding between the serrations when the bit is reacted by a work piece . the movement of the serrated member between the enabled position and the disabled position is controlled by the setting ring so that the selection of both the output torques and the operation modes can be accomplished by a single setting member .