A scissor jack for handling heavy duty work includes four arms hingedly arranged to provide two opposite elbows between a base and a load support, a pair of trunnions, one at each elbow connected by a threaded shaft. One end of the threaded shaft is rotatably engaged in a threaded bush anchored to one elbow on a trunnion to extend beyond the outer corner of the elbow. The jack further includes a movable brace comprising a block slidable on the threaded shaft and carried between a pair of plates which are pivotally secured to the connectors and bent to provide stops for simultaneous location of the arms with spacers on the trunnions to determine the extended position of the jack.