Abstract: This invention relates to a mechanism useful to retain a bi-positionable part in one of its positions so as to prevent inadvertent return of the part to its other position. The unit includes gripping jaws having an open position or status to receive the part in its to-be-retained position, plus weight-influenced members and elements to close the jaws to secure the part. The release or unlock mode of the unit is capable of being remotely effectuated by movement of the part in an over-run phase so as to actuate the jaws to release position for freeing the part. The unit is so constructed as to be compact, self-contained and easy to operate and maintain.