Adaptor for a needleless access device and method for connecting said device thereon

An adaptor for connecting a drug delivery device to a needleless access device provided with a straight external thread, the adaptor comprising:

• a globally tubular body having a proximal region and a distal region, said proximal region being provided with an engagement element for mounting said adaptor on the drug delivery device, said distal region being provided on its inner wall with an internal thread intended to cooperate with said external thread on a determined length of said internal thread so as to connect said needleless access device to said adaptor, said internal thread having on a distal part of said determined length, said distal part having a first length, a first major diameter of constant value mating that of said straight external thread, wherein said internal thread has on a proximal part of said determined length a second major diameter, where the second major diameter is smaller than the first major diameter, wherein said internal thread further comprises a tapered threaded portion linking said proximal part to said distal part, said tapered threaded portion having a second length, the internal thread being configured to increase the friction between the straight external thread and the tapered threaded portion and the proximal part of this internal thread, the proximal part, the tapered threaded portion and the distal part of the internal thread being configured to cooperate simultaneously with the same straight external thread of the needleless access device, wherein the ratio of the first length of the distal part to the second length of the tapered portion ranges from 0.9 to 1.1.