An international standard empty ink cartridge that can be used many times. You can use your favourite bottled ink with a cartridge type fountain pen. Use an injector (sold separately) to suck from the ink bottle and inject it into an empty cartridge.

Note: 'International Standard' cartridges are a common pattern in use by most European and Japanese fountain pen manufacturers. Fountain pens designs will adopt one of two approaches for cartridges: proprietary designs (from the same brand), ensuring they receive the ongoing income from refills; or the standard design, which gives you a choice of cartridge brands to use in your pen.