Abstract: A locking mechanism is disclosed for use on the legs of a jack-up offshore platform. Each chord of the legs includes a rack for cooperation with pinions used in raising and lowering the legs. The locking mechanism of the invention includes a rigid frame attached to the hull of the platform and housing a plurality of vertically aligned toothed chock segments adapted to engage the teeth of the rack on a leg. The chock segments have upper and lower inclined surfaces which cooperate with upper and lower movable wedges for supporting the chock segments. The design makes the chock segments sufficiently adjustable for independent alignment and engagement of the teeth of each chock segment with the corresponding teeth of the rack. Dimensional variances in the rack teeth spacing, resulting from manufacturing tolerances, thereby are accommodated and force concentrations between the rack teeth and chock teeth are minimized.