A portable power drill (11) is disclosed having a chuck or drill collar (14) at one end and a substantially cylindrical (or frusto-conical) twist throttle handle (25, 125, 225) at the other end. Rotation of the handle in the direction of forward rotation of the chuck decreases the drill speed and, conversely, rotation of the handle in the direction of reverse rotation of the chuck increases the drill speed. Consequently, in the event of an auger locked in the chuck becoming jammed, the reaction forces experienced by the drill unit rotate the drill unit in a direction such that throttle decreases the drill speed. In addition, the drill unit is provided with forward (44) and reverse gears (45) and a forward/reverse selection mechanism (48, 50, 51) which is actuated by a forward force, or a withdrawing force respectively being applied to the drill unit via an operator who holds the handles (20, 25) of the drill unit.