Model of fountain pen nib
Generally, pen manufacturers will mark the size and type of the nib on the nib. Generally marked with EF, F, M, B, BB are standard nibs. If marked as OM, OB, OBB, it is the skew tip.
There are five common pen nib sizes, from thin to thick:
EF=XF=Extra Fine The width of the pen tip is approximately: 0.24mm~0.28mm
F=Fine The width of the pen tip is approximately: 0.28mm~0.34mm
M=Medium The width of the pen tip is approximately: 0.34mm~0.44mm
B=Broad The width of the pen tip is approximately: 0.44mm~0.54mm
BB=Double Broad The width of the pen tip is approximately: 0.66mm~0.86mm
Some manufacturers have more subdivided nibs, such as EEF, which is thinner than EF, 3B (Triple Broad), which is thicker than BB, and MF that is between F and M.
Although the definition of the nib size of each brand is not the same (that is, the M tip of the M brand, which may be written thicker or thinner than the P brand), the width of the nib is mostly between 0.18mm~0.86mm
Some manufacturers have oblique nibs in order to match their personal writing preferences, such as: OM=Oblique Medium OB=Oblique Broad OBB=Oblique Double Broad
