Uni-ball eye 0.5 (micro). For lovers of thin but legible and jet-black lines. It is quite fluid, but not as much as the equivalent 0.7, generally a pleasant writing experience (the shape and how well it serves each person's writing style is subjective). It lasts a long time without issues. I commend the company for choosing waterproof ink that does not fade, making it suitable for highlighting with markers and excellent for sketches and watercolor painting!