Individual nib units for the Pelikan M600 are easily interchangeable and well suited for customization. The two-tone, 14k gold nib is available in sizes EF, F, M, B, BB. The M600 nib unit can fit into the M200 and M400 pens, but the nib must be set deeper into the collar. Please specify in the comment box if this nib unit will be used in a M200 or M400 pen.