Indicates the thickness of the pen tip, where EF is the thinnest, f is slightly thicker and m is the thickest. MF is usually unique to Japanese pens, and the thickness is between F and M. In addition, the thickness of different pens is different, and the nominal thickness of each brand is not uniform. ,, and Europe and America are generally thicker than Asia 1 to No.2, that is, the EF in Europe and America is equivalent to the national pen or Japanese MF or even M,,, even if it is the same.

Also, this is only the nominal thickness of the pen, and the actual writing thickness, ink and paper used also have great influence.