Assembly comprising: a drug delivery device comprising a container for a product, said container comprising a distal tip having a longitudinal axis A and a channel defined through said distal tip, said channel providing a passageway for the transfer of said product, said distal tip comprising at least a distal portion and a coupling portion located proximally from said distal portion, characterized in that the greatest external diameter of said coupling portion is greater than the greatest external diameter of said distal portion on a length L measured along said longitudinal axis A at least equal to 1 mm, said distal tip being made of glass, and an adaptor intended to be fitted on the distal tip of said drug delivery device, said adaptor comprising a ring provided with at least one inner projection, said inner projection being capable of cooperating with an outer surface of the coupling portion of said drug delivery device, when said adaptor is fitted on said distal tip, so as to prevent rotational and translational movement of said adaptor with respect to said distal tip, around and along said longitudinal axis A, said ring being radially and outwardly expandable from a rest position, in which said one inner projection defines a first internal diameter Dr of said ring, and a stressed position, in which said one inner projection defines a second internal diameter Ds of said ring, Ds being greater than Dr, said ring being in its stressed position when said at least one inner projection cooperates with the outer surface of said coupling portion, so as to prevent rotational and translational movement of said adaptor with respect to said distal tip. a drug delivery device comprising a container for a product, said container comprising a distal tip having a longitudinal axis A and a channel defined through said distal tip, said channel providing a passageway for the transfer of said product, said distal tip comprising at least a distal portion and a coupling portion located proximally from said distal portion, characterized in that the greatest external diameter of said coupling portion is greater than the greatest external diameter of said distal portion on a length L measured along said longitudinal axis A at least equal to 1 mm, said distal tip being made of glass, and an adaptor intended to be fitted on the distal tip of said drug delivery device, said adaptor comprising a ring provided with at least one inner projection, said inner projection being capable of cooperating with an outer surface of the coupling portion of said drug delivery device, when said adaptor is fitted on said distal tip, so as to prevent rotational and translational movement of said adaptor with respect to said distal tip, around and along said longitudinal axis A, said ring being radially and outwardly expandable from a rest position, in which said one inner projection defines a first internal diameter Dr of said ring, and a stressed position, in which said one inner projection defines a second internal diameter Ds of said ring, Ds being greater than Dr, said ring being in its stressed position when said at least one inner projection cooperates with the outer surface of said coupling portion, so as to prevent rotational and translational movement of said adaptor with respect to said distal tip.