There are those who might be new to fine writing instruments and may not be comfortable yet with fountain pens and want a more familiar Rollerball option. There are also those who know and love their Fountain pens but they wish to have the ability to have a Rollerball for those jobs best suited.

The Schmidt® Cartridge-Rollerball system is an ideal answer to either of the above as it allows for you to take advantage of the 100s of available Fountain Pen inks, either using cartridge, converter or eyedropper methods.

If you want any Mercury Pocket Pen or IKE model with the Rollerball option as the primary or for just $10 additional you can have a swapable section for the rollerball.

https://www.schmidttechnology.de/en/products/writing-instruments-technology-2/fountain-pen-technology-cartridge-rollerball-system/#1536819795380-29dd887f-ca8c