Pilot Refillable 'Converter' Cartridge

For those unfamiliar with a 'converter', these Pilot cartridges can be refilled from any suitable fountain pen ink bottle. This means not only that you can choose from an endless selection of coloured ink, across brands, but also that you will never again depend on buying another cartridge. Indeed this refilling method is far more economical - but bear in mind that it can be more messy and probably a better option when not on the go.