Abstract: A releasable locking device for urging limited relative rotation about a longitudinal axis between a first and second object threadably coupled together so as to maintain a tight connection of the coupled objects. The locking device comprises a brake plate which is supported with respect to the second object so as not to move rotationally relative thereto, a locking plate supported with respect to the first object so as not to move rotationally relative thereto, and a biasing means. The brake plate and locking plate are each positioned laterally adjacent to the first object and each have longitudinally extending complimentary ratchet teeth having inclined surfaces on their mutually facing, surfaces, the inclined surfaces of ratchet teeth of the brake plate being adapted to mate with the inclined surfaces of ratchet teeth of the locking plate.