Abstract: The invention refers to a coupling device for fluid conduits suitable for cases in which uncontrolled tamperings of the coupling ought to be avoided. The device includes a head provided with a coupling thread for a sleeve which incorporates a straight-profiled dentation, while between the sleeve and the head there is a complementary ring provided with another dentation. The dentations are oriented to permit the sleeve to turn in a tightening direction and to prevent it from turning in the opposite direction at the end of the coupling phase by means of angular fixing means consisting of a plurality of lugs arranged on the perifery of the complementary ring. The dentation at the front of the sleeve and the dentation of the complementary ring cover these elements totally or in part.