The Kaweco ballpoint pen refill, in blue, with an M nib, is the consumable for Kaweco Sport line ballpoint pens. This mini-sized refill, compatible with Kaweco Sport line ballpoint pens, replaces the original ink cartridge as soon as it runs out, without needing to replace the entire pen. The M (medium) nib ensures a firm and consistent line, suitable for everyday writing. It's a preferred option for those who already own a Kaweco ballpoint pen and need to refill the blue ink.