These gel pen refills are compatible with Sakura Ballsign iD Series in store: Sakura Ballsign iD PLUS Gel Pen - Silver Metal - 0.4 mm and Sakura Ballsign iD PLUS Gel Pen - Black Matte - 0.5 mm
Ball diameter: 0.4 mm / 0.5 mm
Ink color: Pure black, night black, forest black