TWSBI Eco-T Fountain Pen - Eggplant - Extra Fine NibTWSBI has changed the game! TWSBI Eco T combines simplicity and elegance in this very contemporary fountain pen. By using a piston ink filling system, TWSBI has been able to create a fountain pen with very high ink capacity. What this means is that you no longer need ink cartridges or a converter just fill this high capacity fountain pen and away you go. The Eco T differs from the standard Eco by having a more pronounced grip section; designed with