Method for irreversibly fixing a cap on a container head enabling a limited rotation of said cap on said head

Assembly comprising of a head (1, 1′) and an overcap (30, 30′, 30″, 300), said head having one open end (2) designed to be fixed on the open end of a container or a flexible tube provided with a cylindrical neck (20, 20′) and a shoulder (3) extending from the said open end to said neck, in which the cylindrical neck is provided with at least one helical screw thread (21) with pitch P, and in which the overcap has a cylindrical skirt provided with thread (36) on its inner wall complementary to the thread (21) on the neck (20), characterised in that said overcap has at least one radially flexible and circumferentially rigid axial plate (33), one end of said flexible plate being free, the other end being fixed to the top wall (46) of the overcap at a distance from the centreline slightly greater than the outside radius of the neck, and in that the bottom (10) of the neck is provided with at least one opening stop (12) and at least one closure stop (11) that is not as high, said opening stop being provided with a first wall (14) that gradually moves away from the cylindrical skirt of said neck, such that when the overcap (30) is screwed onto the head for putting the assembly together, the free end of the axial plate comes into contact with the first wall (14) and in that the free end is forced to move centrifugally and is elastically deformed and then, after passing beyond the opening stop, moves downwards towards the cylindrical wall of the neck inside a space between said opening stop (12) and closure stop (11), and in this case its movement is limited by the blocking walls (16 and 17) of said stops (11 and 12).