It is not an M nib but an S nib (Special), a very rare ball nib that Montblanc produced for only one year. It is correspondingly sought-after among collectors and to be valued higher than a standard M. Ball nibs of this kind are particularly suitable for left-handers, since they have lower sensitivity to writing posture. Anyone finding the ink flow too plentiful can store the nib and put a normal M back into the piece.