There are 2 types of the international standard ink cartridges these being the short cartridge which measure 38mm in length and the long cartridges which measure 73mm in length. The only difference is the amount of ink they hold and almost all compatible fountain pens will accept both.
Many major pen manufacturers use standard ink cartridges these include Kaweco, Caran D’Ache, Visconti, Waterman, Waldmann and Faber-Castell. Big brands that have their own design cartridges and will not accept theses universal ones are Parker, Sheaffer, Cross and Platinum. If liquid ink is more your thing them we have a huge selection of Bottled Ink to choose from too.