Parker Refill for Parker Retractable Gel Ink Roller Ball Pens, Medium Conical Tip, Blue Ink, 2/Pack

These are the ones you want: https://www.amazon.com/Parker-1950364-Refill-Roller-Medium/dp/B01GPM3OFO I keep both types onhand because I have certain pens that only work at their best in conjunction with either the metal ones or the plastic ones. The ones in the rainbow packaging (which I refer to as the Originals edition) are the plastic ones with the thicker tip diameter. The plain non-rainbow packaging contains the metal ones that fit into nearly all Parker-style pens.