Replacement O-ring for Bullet Space Pen

If the cap of your bullet space pen feels loose and falls off too easily, there's no need to go and buy a new pen! It's likely you just need a replacement O-ring. This small rubber piece will re-establish a proper seal for the cap.

Note that the small notch on the O-ring is intentional, as this prevents an airtight seal and allows the cap to come off smoothly.