JetPens O-Rings - 9 mm Outer Diameter / 7 mm Inner Diameter - Pack of 5 - Black
Platinum Preppy Fountain Pen - Black - The Goulet Pen Company
Amazon.com : Platinum Preppy Rainbow Fountain Pen Set, Fine Point - Pack of 7 : Office Products
Eyedropper converted my first platinum preppy today! :) It was fairly straightforward, though I should have gotten a slightly smaller o-ring. : r/fountainpens
Platinum Preppy Fountain Pen 02 EF Nib Review — The Pen Addict
Converting a Platinum Preppy to eyedropper. | Fountain pen blog