The invention relates to a front end for an auto-injector, the front end comprising a syringe with an injection needle and a stopper, wherein the syringe is slidably arranged within a syringe retainer, wherein an outer sleeve for preventing access to the needle is removably arrangeable over the syringe retainer, wherein the syringe retainer comprises a screw thread for connecting it to a correspondent screw thread of a mounting of a re-usable auto-injector back end comprising a drive means for advancing the syringe and needle in a proximal direction for needle insertion and for advancing the stopper within the syringe for injection, wherein a resilient locking barb is arranged to rotationally lock the syringe retainer to the mounting in an unscrewing direction when the front end is screwed to the re-usable back end and when the outer sleeve is removed, wherein the outer sleeve is arranged to unlock the resilient locking barb when arranged over the syringe retainer.
