Fineliner Pens
Tip width is printed in millimetres and it is the whole specification, but it only behaves as promised on paper that does not absorb. On a light or fibrous sheet a fine line spreads and the distinction between two widths disappears. The other thing that ends a fineliner early is pressure, since the tip is designed to glide and splays permanently once someone bears down. See pens, markers and notebooks.