The pen nib can be said to be the most critical part of the pen. There are various changes from thin to thick. Generally, the most common pen nib sizes are “B (Broad), M (Medium). Mainly "coarse", FM (Fine-Medium), F (Fine) and EF (Extra-Fine). From thick to fine, they are Bgt; Mgt; Fgt; EF. The pen tip size of each pen manufacturer is There will also be slight differences in specifications. In the same size unit, the nib of Japanese fountain pens will be thinner than that of European fountain pens.

So, the difference between the F nib and the M nib of the fountain pen is that the size of the nib is different. F=Fine, which means the width of the pen tip is about 0.28mm-0.34mm; M=Medium, which means the width of the pen tip is about 0.34mm~0.44mm. The "F nib" pen nib is slightly thinner than the "M nib" pen nib.

According to normal writing habits, Westerners mostly use the M nib when using fountain pens, and use the B nib when signing. Because the strokes in Chinese writing are complicated, F or thinner EF pen tips can generally be used.