The Rotring Rapidograph uses a cartridge, and there is technical language, which I won't attempt to repeat, that says in essence-- lit
Rotring Rapidograph Technical Drawing Pen - 0.10mm
Review: Rotring Isograph Pen vs Rotring Tikky Graphic // How to Unclog Rotring Isograph
Rotring Pens I bought: Isograph 0.5 & 0.7
Rotring Rapidograph FOR SALE! - PicClick
Needed a Pen that I could Drag Across a Ruler Without Marring Nibs. But I am Too in Love with Fountain Pen Inks to Use Just Any Pen. Solution: Rotring Isograph 1.0mm
Rotring Isograph Master Set
Rotring Isograph Technical Pen, 0.10 mm
The Best Set of Black Disposable Drawing Pens for Artists and Writers
rOtring Rapidograph Pen -Technical Pen/Home Delivery