Abstract: A pair of spring connected jack members have opposed faces. One of such members has one or more longitudinally extending ramps engageable by pinion gears or the like secured on cross shafts movable freely between the two jack members. Also supported on the cross shafts but for free rotation on such shafts are pairs of rollers engageable with tracks on opposite faces of the jack members. The tracks are parallel with the ramps and are offset from each other in an arrangement such that one of the rollers in a pair engages one of the tracks on a first of the jack members but is disengaged from the opposite jack member and the other of such roller in the pair engages the track of such opposite jack member but is disengaged from the first jack member. The cross shafts have wrench engaging ends for rotating the pinion gears so that they will travel along the ramps to expand or contract the two jack members relative to each other.