The invention relates to an adaptor (1) for connecting a drug delivery device (100) to a connector (200) provided with an external thread (201), the adaptor comprising a globally tubular body (2) having a proximal region (2a) and a distal region (2b), said proximal region being provided with engagement means (3) for mounting said adaptor on the drug delivery device, said distal region being provided on its inner wall with an internal thread (5) intended to cooperate with said external thread so as to connect said connector to the adaptor, said internal thread defining an internal thread crest (5a), characterized in that said internal thread crest is provided with at least one deformable radial end part (6) configured so as to be radially deformed when said connector is screwed into the adaptor.The invention further relates to a drug delivery device comprising such an adaptor and to a method for connecting the connector to the adaptor.
