For a long time I thought it was sad that I could not use my Rotring 600 fountain pen more than I did. It would always dry out between times of use. I have simply never been a fountain pen guy. At the same time the plastic quality of my favourite writing and sketching instrument, the BIC M10, has become more fragile so I often break the clip. A simple modification later, my Rotring can use the BIC cartridges. The best of two worlds!