Abstract: Impregnable locking system of the fastening of display-boxes called "blisters", consisting of a box in two articulated halves having on the side opposite their hinge fastening flaps destined to be held one against the other by this system, characterized in that it consists of a clip destined to cover these two flaps, and between which is attached a transverse shaft, a vertical notch made in the flaps allowing this shaft to go through when the clip is put into place, two gears which being slid onto this shaft, between the outer side of each flap and the corresponding side of the clip. A device is provided so that these gears are constantly pushed towards each other, and once this clip is placed on the flaps, the gears come to rest in lodgings made in the outer sides of the flaps, thereby immobilizing the clip onto the flaps.