the drive sleeve 14 continues rotating by contrast fig7 c shows the drive sleeve 14 and the shroud 3 during removal of the auto injector 1 from the injection site in the course of an injection cycle the shroud 3 is translated in proximal direction p to an extent bringing the teeth 14 1 and the splines 3 8 into engagement even though the forward extension of the shroud 3 is limited by the position of the drive collar 13 the auto injector 1 is configured to provide needle safety at all stages of the operational cycle with a transmission ration of 1 or less as illustrated as the needle is inserted into the injection site the drive collar 13 moves in sync with the syringe 5 therefore given that the needle 6 is initially fully covered when the shroud 3 is fully extended and the needle 6 moves in sync with the drive collar 13 the needle can not protrude a greater distance from the shroud 3 than the distance permitted by the drive collar 13 and the inward protrusions 3 5 if the transmission ratio were greater than 1 the design may be modified to position the needle 6 further from the proximal end of the shroud 3 to ensure.