Kaweco Ink Cartridges. Short international standard cartridges suitable for all Kaweco fountain pens and a wide range of other fountain pens. Pack of 6. These cartridges are designed for a smooth writing experience and come in a classic royal blue color. They are compatible with Kaweco fountain pens and many other brands that use the international standard format. Each pack contains 6 cartridges, with each cartridge holding 1 ml of ink. Kaweco has been producing quality writing instruments since 1883, with a focus on functionality and service.