a pistol grip drill has two control triggers on its hand grip . one trigger controls power to a motor in a casing of the drill and the other trigger initiates a sequence which interchanges the positions of two chucks . the chucks are mounted on a forward extension of the casing . the extension has two degrees of freedom . it is firstly capable of rotating through ninety degrees about the axis of a pivot to bring the unused chuck to the driving position in front of the casing . the second degree of freedom allows the extension to be then rotated about the driving axis of a drill drive shaft so that the displaced chuck is moved from an upwardly - pointing position to a downwardly position directly in front of the pistol grip . the interchanging of the chucks can be controlled by the hand of the user holding the hand grip .