Ink Roller Cartridge 881. For Cartridge Rollerball Pen Base Up and base ball base: 34 x 34 cm. Control Cartridge with wear-resistant stainless steel tip. Ink not erasable. Free Ink System. With visible ink level and ink regulator for even strokes from start to finish. Line width: 0.5 mm writing colour: Blue. Contents: Box of 5.