Istvan, the 18k M-CI nibs are 0.8mm. But they write slightly wider than the steel M-CI (I have both) mostly because the gold nib is softer & writes a much wetter line. The 1mm B-CI is probably what you're looking for.
In other news, Mr. Masuyama did reply, and 2 of my nibs are now on their way to be modified!
Thank you for this review "cyranodb".
While trying to look up all information & reviews of the FC pens I chanced on yours.
Love that smoked demonstrator look.
The pen I am waiting to be made is the smaller model 03 in the Black & Maroon version , with no clip.
I'm very familiar with Mr. Masuyama's excellent work on nibs & have two of his wonderful italics ground from 14K Sailor MS nibs.
I'm curious how wide Mike's 18K JoWo M-CI is. I am looking for a fairly wide 0.9 or 1.0 italic in 18K.