An injector for delivering a liquid medicament is provided. The injector comprises: a housing having an opening at a first end and a cartridge contained within the housing, wherein the cartridge comprises a first fitting mechanism which is directed outwards from the opening of the housing； a removable cap； and a needle assembly supported on the removable cap, wherein the needle assembly has a second fitting mechanism which is directed outwards from a distal end of the removable cap, the removable cap being further configured such that each of the distal end and the proximal end of the removable cap are engageable with the opening of the housing,wherein the first fitting mechanism is complementary with the second fitting mechanism such that the needle assembly is connectable to the cartridge by joining the first and second fitting mechanisms.
