The Kaweco black M ballpoint pen refill provides smooth, even, and quick-drying writing in the standard D1 multi-function format. Made with a slim, high-precision metal body and a medium-sized M ballpoint tip, it uses oil-based ink that won't bleed or smear on paper. It is compatible with Kaweco Sport, Liliput pocket pens and other writing instruments that use the universal D1 standard system. The classic, high-density black color is indispensable for signatures, filling out forms, and continuous professional use.