In a previous patent application of the same applicant a valve or stopcock for fluids was proposed comprising a body, a swivel shutter in said body between a closed position and an open position, a control rod for said shutter, and a throttle or clamp lover keyed to said rod for the rotation of the shutter. The throttle or clamp lever is fastened axially on the rod by means of a lock screw that is tightened in a threaded hole envisaged at the top of the rod itself. In order to prevent uncontrolled disassembly of the throttle or clamp lever, the lock screw ! s configured to be tightened and loosened only using a specific tool at the disposal only of whosoever is charged with managing the use or non-use of the valve to prevent tampering or frauds.

According to a preferred embodiment of this invention, the lock screw has 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 the polygonal head, and the tool for turning said screw has at least two expansible elastic jaws to widen and extend in an axial direction the

base extending over the dome on the head of the screw and then contractile to engage the perimeter surface of the polygonal head of the screw.

The putting Into practice of the model presented here, however, has shown that with certain tools or utensils different from that envisaged, it is nonetheless possible, albeit with difficulty, to loosen the lock screw by locking onto the base of the dome that extends over the polygonal head.

The purpose of this invention is to provide a perfected anti-fraud lock screw that in fact prevents any loosening attempt, with any tool or utensil, and consequently tapering with the valve or stopcock to which it is fitted.

This purpose is achieved by means of a screw that fastens a throttle or clamp lever at 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 axis of the screw, above said polygonal head.

An example of practical embodiment of the anti-fraud screw in question will be described hereunder with reference to the attached drawings, which are approximate and not limitative, in which : Fig. 1 shows a valve with throttle or clamp lever and relevant anti- fraud retention screw separated ; and

Fig. 2 shows, in longitudinal section, the anti-fraud retention screw according to the invention.

Fig. 1 approximately shows a ball valve, the body 11 of which encloses, in a known manner, a round shutter-not shown-to which is connected a swivel rod 12 by means of which the shutter can turn by 90"between a fluid transit opening position and a closing position. For such rotation, to the rod 12 is keyed a throttle or clamp lever 13. This is axially fitted on said rod 12 by means of a retention screw 14 that screws up into a threaded hole 12' envisaged at the top of the rod.

The retention screw 14 consists of a threaded shank 15 with a polygonal head 16 surmounted by a truncated-cone shaped dome, semi-spherical or of other shape with a base 18 which extends over the edge of the polygonal surface 16 of the head. The base 18 that extends over the edge of dome 17 prevents access to the polygonal head 15 of the screw for the rotation of this by means of a standard polygonal tubular spanner. Access to the polygonal head 16 of the retention screw 14 is thus only possible with a tool 19 having at least two lock jaws 20 each with a flat inner section 21 corresponding to a face of the polygonal head of the screw. The jaws 20 of the tool are elastic and such as to expand to extend the base 18 that extends over the edge of dome 17 when the tool is pushed with force on the screw head to engage with their flat inner sections 21 the faces of the polygonal head of the screw for the rotation of the latter. On the other hand the tool can be separated from the screw head by forcefully moving it away from this.

According to the invention, the dome 17 is free to rotate around the shank 15 of screw 14 above the polygonal head 16 which on the other hand is integral with shank 15. For example, the polygonal head 16 can consist of a nut screwed onto the shank 15 of the screw and secured to this by gluing, while the dome 17 can be made of a ring-shaped section part substantiate trapezoid located above said nut and held around the shank 15 by an edging 15 envisaged at the top end of this To glue the nut, an anaerobic adhesive can be used such as Loctite.

This way, only by using the special tool 19 is it possible to loosen or tighten the threaded shank 15 of the screw 14 by adjusting nut 16, while if the dome 18 is engaged with any tool or utensil, no effect is achieved as this rotates freely around the threaded shank.