A jack assembly including a telescopic column driven via a gear box, wherein: the gear box is coupled to a rotary input of a drive mechanism that extends and retracts the column; the gear box has only a single input gear and a single output gear that is coupled to the drive mechanism; and the input gear has a connector adapted to be engaged and driven by a portable, hand-held power tool. The invention also relates to a jack assembly with a gear box for use as a jockey wheel for attachment to a towed vehicle, to raise and lower a draw bar of the vehicle.