The only "Swiss" threads I've ever seen on a bike are the left hand threads on the bottom bracket fixed cup which are M35x1.0 LH.
I'm not sure that all Swiss bikes used LH fixed cups. Some French bikes did - on occasion.
Everything else should have standard (French) metric threads.
A year ago I bought a late 60s Andre Bertin on eBay. It was complete except for wheels and all original except for an aluminum alloy Shimano 600 headset. I had the correct Stronglight P3 headset and I figured it would be nice to have a metric alloy headset to use later on an OT frame.
I was a... surprised when I removed the top adjustable cup. It was an inch size headset! Someone used a thin piece of plastic for a shim to make up the difference between 25mm and 25.4mm (1").
Since it was an aluminum cup with plastic shim there was no damage to the steerer threads.
A 1" x 24 TPI size adjustable cup can be screwed about 5-6 threads onto a 25mm x 1mm pitch metric steering tube before the threads lock up. Then some hammer mechanic can force it to go on further which usually damages the metric threads but they can still be used with a proper metric headset.
BTW, The correct internal diameter for a metric steering tube is 22mm to fit a 21.9mm stem but 22mm became the French standard stem diameter by default (Cinelli, 3TTT, ITM and others).
I've seen French steering tubes with an ID that was almost 22.2mm and I've run across British and Italian bikes with steerers under 22.2mm.
I attributed these to very loose manufacturing tolerances rather than any intentional design!
Chas. Colerich Oakland, CA USA
Rnitro1969@aol.com wrote:
> greetings.
>
> i picked up a mondia special
> serial # 153546 late 60-70's ?
> the bottom bracket seems fine
> with french stronglight
> but the head set crown race is not
> snug and the top cup is loose.
>
> is this a swiss thread thing.
>
> thanks
> robbie fellows
> lakewood,ca. usa