Fountain pen cartridges come in the widest range of types. The common pen cartridge is the international standard, a 38 mm cartridge closed by a small glass ball. This and the international standard long, a 72 mm cartridge, are common in European-made pens. Many pen manufacturers also produce their own proprietary cartridges, a few of which will work in other pens. The proprietary Parker cartridge is a little longer than the international standard and tapered at one end. Shaeffer is a medium-length cylindrical cartridge; Shaeffer Slim is a slightly longer tapered cartridge. Cross is a short tapered cartridge with three "steps" along its length. Cartridge pens may be fitted with a converter to fill from a bottle of ink.
While most ballpoint ink pens are disposable, some higher-end models take a cartridge. These pens tend to be comparatively costly, and can be made from wood, precious metals or even stone and antler. Ballpoint pens take two main types of cartridges: the "Cross-type," similar to that used in Cross brand pens, and the slightly thicker Parker type. Cross refills hold slightly less ink, but are more suitable for very slender pens.
Mostly-disposable rollerball pens provide a smoother writing action than many ballpoints. These pens use a wide variety of cartridges, mostly Schmidt-type. Some rollerball pen manufacturers produce their own proprietary cartridges, especially for extra-small or unusually-shaped pens.
Over the years, nearly all refillable pen manufacturers have produced proprietary cartridges and pens that require them. Many vintage pens require a specific cartridge; this is particularly true of compact pens. According to Franklin Christoph, a fine pen retailer, old Aurora, Duke and Uranus brand pens are also likely to require special cartridges. In some cases, replacements are not available. Pen owners must use a syringe to fill the empty cartridges with bottled ink.