Drone's post above states, The 3776C F nib provides more options, but is still quite fine True!
The F nib on my Chartres Blue is just a tad finer than the Sailor 1911s F nib. Not by much, but it is a well defined thin line.
I think the Platinum Fine is around 0.28mm to 0.29mm=that is just my guess from using some Platinums. The Preppy fine is 0.3 and my Chartres is a finer line than the preppy.
So far the pen likes any ink I use and only on the worst papers does the fine nib require a very light touch.
I have had the pen for a year now and it has been flawless.
If need be, PM me your address and I will write you a little letter and mail it to you. This way you can see for yourself.