Abstract: The lock comprises: a fixed bush which defines a cylindrical cavity within which a cylinder rotating about the longitudinal axis of the cavity is mounted; a spring for retaining the cylinder within the cavity in the axial direction, the spring being interposed between a first circumferential groove made in the external lateral surface of the proximal portion of the cylinder and a facing slot made in the wall of the cavity; and interference means suitable for preventing the rotation of the cylinder within the cavity when the cylinder is pushed towards the distal extremity of the bush. A plurality of circumferentially spaced reliefs, extending each for an arc of a circle, radially protrude from a circumferential section of the external surface of the proximal portion of the cylinder, which reliefs bear in normal conditions against a circumferential flange which radially protrudes inwards from the internal surface of the bush.