Pen injector parts

• Disposable pen needle with a large outer cap and a small inner needle cap
• Cartridge filled with medicine
• Cap that covers the rubber stopper between uses
• Window or area to view the dose
• Dial or knob to adjust the dose
• Button to give the shot

Many pen injectors come prefilled with the cartridge of medicine. You can refill and reuse some kinds of pen injectors by placing a new cartridge of medicine in the pen.