The new Kaweco Classic Sport Piston Filler Fountain Pen is finally here. The nib sizes available are Extra-Fine, Fine, Medium, Broad, and Double Broad, but please note that the nib used for this pen is not interchangeable with other Kaweco Sport pens. Since 1883, there have been various methods for filling fountain pens. While ink cartridges are now the most popular, in the past, ink bottles were used. The piston mechanism, introduced in 1937 with the #612 version of the Kaweco Sport fountain pen, has proven to be the most reliable filling system. This writing instrument features an integrated reservoir that allows ink to be drawn directly from a glass bottle, eliminating the need for ink cartridges. The transparent window also allows users to monitor the ink level at all times.