Abstract: The fastener for chains, necklaces, bangles and similar pieces of jewelry comprises a main body connected by one end to the piece of jewelry, with this main body being cut out in a central area and supporting a heel extended by a spindle on which is pivotally mounted a square shaped rocker having a vertical arm which is submitted to bias of a spring-blade. In the rest state of the rocker, said rocker cooperates with a hook shaped end of the main body for maintaining a mobile free end of the piece of jewelry. Said main body is enclosed in a case provided with vertical side walls having windows with a cross-piece of a substantially H-shaped mobile part sliding therein.