A locking device interacting with a drive member and including an inner tube and an outer tube; where the inner tube has a first free end that projects from, and is axially displaceable from, a first end of the outer tube; where there is a locking member on the other end of the inner tube, said locking member providing the means whereby the inner tube and the outer tube can be releasably locked in various axial positions relative to each other; where the locking member includes a tubular locking sleeve that is slotted by at least one axially aligned slot and a wedge that includes wedge surfaces, the wedge surfaces being, when acted upon by a drive member, displaceable along and relative to interacting wedge surfaces of the locking sleeve, such displacement pressing the locking sleeve against the outer tube, the inner tube and the outer tube.