An attachable needle assembly (102) for use on a medication delivery pen (104), the needle assembly (102) comprising a housing (110) enclosing a hub (106) having a communication needle (108) configured to engage the medication delivery pen (104) and pierce a reservoir septum of the medication delivery pen (104), a communication septum (172, 176) of the needle assembly (102) defining a septum chamber (180, 182) that is in fluid communication with the communication needle (108), a plurality of needles (118) disposed in the communication septum (172, 176), a follower ring (130) that determines which needle (124) of the plurality of needles (118) is to be selected, and a snap ring (136) that exposes the selected needle (124) and moves the selected needle (124) in fluid communication with the septum chamber (180, 182), wherein when the housing (110) is in a first position, the plurality of needles (118) is not exposed, and when the housing (110) is in a second position, the selected needle (124) is in fluid communication with the septum chamber (180, 182) and exposed for medicament delivery.
