the upper closure element 12 and an upper surface 26 of the lower closure element 14 form a recess 28 containing a rectangular parallelepiped shaped slide 30 see fig1 a along two planes of symmetry of the slide passing respectively through the main axis xx u2032 and an axis yy u2032 perpendicular to the main axis xx u2032 the slide 30 is integral with one 36 of the two second walls of the opening 20 perpendicular to the main axis xx u2032 through the intermediary of a spring 46 with an axis of elasticity parallel to the main axis xx u2032 the slide 30 comprises a hole 44 with an axis vv u2032 perpendicular to the plane s of the sandwich the axis vv u2032 of the hole 44 is offset on the spring 46 side by a certain distance from the axis yy u2032 of the slide the slide 30 is kept in position in the recess 28 by an inertial screw 40 inserted in the hole 44 of the slide the inertial screw is itself integral with the lower closure element 14 fig2 a represents a partial view of the device in fig1 a in longitudinal section along a plane p parallel to the main axis xx u2032 of the central element 10 and passing through the axis vv u2032 of the hole 44 of the slide 30 fig2 b and 2 c show respectively a top view and a front view of an inertial screw of the device in fig1 a the circular cylinder shaped inertial screw 40.