A coded cartridge holder system is disclosed for use with a cartridge assembly (20) containing a fluid and a delivery device (10), where the system has keyed connectors (5, 5&prime, 6, 6&prime) to prevent accidental attachment of the wrong fluid delivery device (10). The system comprises a coupling (1) attachable to the dose setting portion (12) of the device (10) and keyed to the proximal end of the cartridge holder (14). The cartridge holder (14) may also contain medical coding (27, 28) to correspond to matching coding (27&prime, 28&prime) on the distal end of a cartridge assembly (20).
