According to:
http://www.thewritingdesk.co.uk/reference.php?id=5- NP (needlepoint). A very small point to give an extremely fine line. Sometimes referred to as XXF or EEF (extra-extra-fine).
- EF (extra-fine). A nib that will give a line width of around 0.4mm. Suitable for those with very small writing.
- F (fine). A nib that will give a line width of around 0.6mm. Suitable for those with small writing.
- M (medium). A nib that will give a line width of around 0.8mm. Suitable for those with average-size handwriting.
- B (broad or bold). A nib that will give a line width of around 1.0mm. Suitable for those with large writing or for signatures.
- BB (extra-broad). A nib that will give a line width of around 1.2mm. Suitable for those with very large writing or for signatures.
- BBB or 3B (extra-extra-broad). A nib that will give a line width of around 1.4mm. Will give large flowing lines and usually good variation between down-strokes (wide) and side-strokes (less wide).
- OM, OB etc (oblique). A nib ground so that the tip slopes to the left, rather like your left foot. Designed for those writers that either rotate the pen anti-clockwise or hold the pen at an unusual angle. Note that oblique nibs do not normally give more line variation than a standard rounded point unless specifically stated otherwise.
- ROM (reverse-oblique medium etc). A nib ground so that it slopes to the right, rather like your right foot. Sometimes suitable for left-handed people. Sometimes confusingly called right oblique. Uncommon.
- LH (left-hand, eg Pelikano and Lamy). A medium nib but with the point shaped so that it may be more suited to left-handed writers, particularly those who hold their above the line of writing ("over-writers").
- MK (rounded medium). A special nib made by Lamy with a more rounded point such that the orientation of the pen relative to the paper is less critical than a standard point and therefore easier for beginners. The designation is no longer used but the current Lamy medium nib is made to the same specification as the MK.
- A. A rounded point made by Lamy for the abc school pen. Between fine and medium.
- Italic (eg IM, IB, 1.1mm 1.5mm etc). A nib ground so that the tip is flat instead of rounded. Designed to give extreme line variation between wide down-strokes and narrow side-strokes in the manner of a calligraphy pen. Often specified in terms of width (in mm). Most factory-produced italic nibs are actually stub- or cursive-italics meaning the corners of the nib are rounded so allow continuous writing unlike a proper calligraphy nib that requires much greater care.
- Stub. A more rounded, gentle version of an italic nib such that good line variation is produced. Like italic nibs, these are usually specified in terms of width (in mm). Less demanding in terms of angle to the page than an italic or stub-italic nib.
