An upright frame is secured to the base member of a rock crusher and supports a slide bar for horizontal movement. A fluid-operated cylinder is connected between the upright frame and the slide bar for driving the latter longitudinally in both directions, and a pivotal driver is mounted on the slide bar for movement into and out of engagement with projections on the crusher bowl. A second fluid-operated cylinder is connected between the slide bar and the driver for pivoting the latter between an inner engaging position with the projections and an outer release position. By suitable operation of the two fluid-operated cylinders, the bowl can be rotatably driven on threads on the base member for installing it and removing it. An upright extension is attachable to the slide bar and carries an auxiliary driver thereon disposed above the main driver so as to engage the projections on the bowl when such projections are above the plane of the main driver such as when installing or removing the bowl. A jam nut is employed to lock the bowl non-rotatably on its base member and such jam nut is driven by a fluid operated cylinder having adjusted mounted positions for repositioning such cylinder in the event of thread wear.