One thing to bear in mind about French headsets is that only the the adjustable (top) cup and the locknut, and perhaps the keyed washer is different. French bikes had the same head tube ID as English/Italian, so the pressed cup and the pressed top race are identical regardless of headset threading. Crown races vary in dimension, usually 26.4 or 27.0, but this is not a function of nationality. Both 26.4 and 27.0 will be found with English, French and Italian headsets. When Mike Kone had Bicycle Classics, he used to sell a Campy NR HS French "kit" composed of French threaded top cup and locknut and the washer with the flat.
Regards,
Jerry Moos
> ----- Original Message -----
> >
> > Daniel Artley wrote
> >
> > > Can anyone suggest how I can determine if I do not have a headset of
> > > fork that I know are French?
> >
>
> French steerers are 25.0mm in diameter, vs the 25.4mm for Italian/ISO.
Even
> the cheapie plastic vernier calipers can measure that well enough to tell
> quite easily.
>
> If you only have the headset, it will be harder to tell, though I suppose
> the thread ID should be pretty consistent between the standards.
>
> Jon Schaer
> Columbus, OH