| 摘要 |
A theft-resistant fastener system includes a rotatable wrench adapted to engage a head portion of a fastener and to rotate that fastener and head portion about a fastener axis. The wrench and fastener jointly have at least three ball-and-socket joints distributed about the fastener axis. Each of these ball-and-socket joints has a ball in the wrench and a socket in the head portion of the fastener, with each socket being provided with a circular cross-section about a socket axis extending at an acute angle to the fastener axis. The wrench has a releasable actuator for pressing the balls into the sockets preparatory to and during rotation of the wrench about the fastener axis. The head portion of the fastener is prevented from clearing the balls, when the actuator presses these balls into the sockets, by providing that head portion at each socket with an overhang extending over part of the ball in that socket. A need for means for biasing the balls out of the sockets upon release of the actuator is avoided by providing each overhang with an outer limit closer to the fastener axis than a center of a corresponding one of the balls of the ball-and-socket joints. Actuation of the fastener by a conventional wrench is prevented by providing the head portion with outward slopes at the sockets and otherwise about the fastener axis.
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