An assembly for a drug delivery device (1) is provided the assembly comprising a cartridge (2) adapted and arranged to contain at least one dose of a drug (7), a bung (10) being slidably arranged within the cartridge (2), a housing (3) comprising a distal end and a proximal end, and a piston rod (11) adapted and arranged for moving the bung (10) in the distal direction with respect to the housing (3) for dispensing a dose of the drug (7). The assembly further comprises a drive member (13) adapted and arranged for transferring movement to the piston rod (11) for dispensing the dose, and - an engagement member (18) configured to mechanically cooperate with the piston rod (11) and with the housing (3). The engagement member (18) is moveable between a reset position, where the engagement member (18) is allowed to rotate with respect to the housing (3), and an operating position, where the engagement member (18) is rotationally locked with respect to the housing (3), wherein the assembly is configured such that the engagement member (18) is rotated and simultaneously axially displaced during movement of the engagement member (18) between the operating position and the reset position. The engagement member (18) and the housing (3) are threadedly engaged with one another, wherein at least one of the engagement member (18) and the housing (3) comprises a thread and the other one of the engagement member (18) and the housing (3) comprises an interaction. Furthermore, the use of an engagement member (18) for a drug delivery device (1) is described.Linvention concerne un assemblage pour un dispositif (1) dadministration de médicament, lassemblage comprenant une cartouche (2) conçue et disposée pour contenir au moins une dose dun médicament (7), une bonde (10) disposée de façon coulissante à lintérieur de la cartouche (2), un boîtier (3) comprenant une extrémité distale et une extrémité proximale, et une tige (11) de piston conçue et disposée pour déplacer la bonde (10) dans la
