TWSBI ECO fountain pens have stainless steel nibs and use a piston filling system. The barrels are clear so you can see the amount of ink and the cap includes an inner cap that provides a perfect seal when the pen is not in use. Note: Please take care if removing/adding the nib as it is very fragile. **Every pen will be unique in pattern variation, as these patterns are completely random during the injection process and cannot be chosen. How to Choose a Nib Size: If you write small, go with Extra-Fine For everyday use, Fine is a great choice If you tend to write on the larger size, Medium is perfect and does provide a smoother ink flow Bold is for statements – Sign a check, write a header or show off your shimmering/sheening ink Stubnibs are used for an italic/calligraphy writing style with the down strokes being wide and the side strokes thin.