| 摘要 |
This invention concerns a screw for the anti-fraud locking of a throttle or clamp lever on the control rod of a valve shutter or stopcock, comprising a threaded shank having a polygonal head surmounted by a truncated-cone shaped dome, semi-spherical or of other shape, the base of which extends over the edge of the perimeter surface of said polygonal head, where said dome is free to turn around the shank above said polygonal head, so that only by means of a special tool can the threaded screw shank be tightened or loosened by means of the nut, while by operating on the dome with any tool or utensil, no effect is achieved as this is able to turn idly around the threaded shank.
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