A coded cartridge holder for use with a drug delivery device is provided. The cartridge holder includes a fastener that becomes operative based in part on a length of a cartridge or a diameter of the cartridge. In one embodiment, the cartridge holder is coupled to the drug delivery device. The cartridge holder comprises a first blocking feature. The drug delivery device includes a cartridge detector comprising a second blocking feature. This feature may be a pin, for engagement with the first blocking feature of the cartridge holder when the cartridge acts on the cartridge detector. The cartridge holder may further include a fastening mechanism configured to fasten the cartridge holder to the drug delivery device only when the second blocking feature engages the first blocking feature.