The Kaweco pen refill, in red (Ruby Red), with an M nib, comes in a box of 6 units. These short ink cartridges, in the international standard format, are compatible with most fountain pens that accept this system, including models from brands such as Pelikan, Faber-Castell and Diplomat, as well as Kaweco pens themselves. They come in a box of 6 units, ready to replace as soon as the ink runs out, without needing to refill the pen from an inkwell. It is a preferred option for those looking for a vibrant and classic red in their fountain pens.