Abstract: Socket for reservoir or container, able to be associated to a specific nozzle which fills reservoir or container with suitable substances, provided with a mechanical device for avoiding the introduction of substances of nature different from those of the specific nozzle, characterized by fact that said device comprises a socket closure system maintained in the closure position by blocking means, that in the same socket deblocking means are present which are activated by means of the introduction of the specific nozzle having the external diameter section corresponding to that of internal section of the socket where the deblocking means are placed.