Abstract: Correspondingly keyed combination of a round-headed bolt fastener and a generally cylindrical socket, preferably for use in securing an automobile wheel cover against theft. The fastener has a plurality of axial slots, or lock impressions, about the periphery of the circular head which may be spaced in accordance with a preselected code. The wrench socket is provided with a corresponding number of key elements projecting inwardly from the cylindrical wall of the socket, the position of the key elements being in accordance with a preselected code. When the key code of the wrench matches the lock code of the fastener, the wrench socket may be slipped over the fastener head with the key elements engaging the lock impressions so that the wrench may tighten or untighten the fastener. The fastener has an axial recess extending from the outer face of the head with an inner beveled surface about the recess opening.