A cartridge unit (300) for a drug delivery device (1) is provided, comprising: a cartridge unit guide feature (327), the cartridge unit guide feature being provided to mechanically cooperate with a housing guide feature (351) provided on a housing (10, 350) to establish a guiding interface in order to guide relative movement of the cartridge unit and the housing when attaching the cartridge unit to the housing, wherein the cartridge unit guide feature is provided with at least one cartridge unit interface feature (330), wherein the cartridge unit interface feature is adapted to establish a further interface with the housing.
