| 摘要 |
The screw has a head (12) provided with device enabling it to be rotated and a threaded shank (14). The head has the shape of a disc of diameter (D) greater than the root diameter (d) of the threaded shank. On its periphery are two raised zones (18,20) separated from the shank. These zones each have axial engaging faces (18a,20a) and ramps (18b,20b) opposite these faces. The two faces are located diametrically opposite so as only to allow an engaging tool (24) to rotate in a single rotational direction (R1) of the screw. The engaging faces are turned in the direction (R'1) opposite to the direction (R1) in which the screw thread (16) is wrapped round from the head and the ramps are inclined in the same direction as the thread.
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