Abstract: The ring is composed of three arc of a circle-like portions which are hinged connected between them so as to allow their mutual pivoting movement in the plane of the ring. The first portion (1) extends on an arc of about 270.degree. and each one of the two other portions extend on an arc of about 45.degree., providing a full ring. Male locking member (9) and female locking member (10) allow to close the ring between the first portion (1) and the third portion (5). To open the ring, it is enough to push inwardly the hinged connection (7) between the second and third portions (4, 5) of the ring, against the resilient force exerted by the first portion (1). The closure of the ring takes place in engaging the male locking member (9) into the female member (10) and by displacing outwardly the hinged connection (7) also against the resilient force of the first portion (1). Once the ring is closed, it is no longer possible to cause its opening under the action of an outwardly directed force.