Rotring 600....rollerball with cartridge. Never seen before. The rollerball mechanism is permanent and doesn't remove. That one replacement cartridge came with it. Anyone seen these before? What do I refill it with? :
Rotring 600 Ballpoint Pen - 1.0 mm - Black | JetPens
Rotring 600 Full Metal Blue 0.5mm Mechanical Pen (2114266)