Fred Rafael Rednor wrote: If the steerer is built to French specifications, it's 25mm in diameter rather than 1 inch (i.e. 25.4mm), although people sometimes also refer to the French spec steerer as "1 inch". I would say that it's _nearly_ certain that the headset on this bicycle is French threaded. The reason I would not say it's 100% certain is because of an astounding experience I had this past weekend. I was working on a lightweight Peugeot from the same period as your Motobecane and found that the steerer tube was threaded for an English headset. Nevertheless, the inside diameter of the steerer was 22mm - i.e. the French standard. This was the opposite of my previous experience with "mixed-spec" steerers. That is, in the past I've worked on French bikes whose steerer tubes had French threading although the inside diameter would take a 22.2mm (i.e. "rest of the world") stem. I still have not fully recovered from this experience. Cheers, Fred Rednor - Arlington, Virginia +++++++ Perhaps I can compound the misery. Steerer diameters are nominal. For example, just measured an (OT Cannondale) at 25.35 instead of 25.34. Explanation is that the tops of the threads are flat or rounded, not carried up into a sharp V. Should still be able to pick up the difference between FR. and Real World (whoops), since the undersizing is only about 4- 6 thousands.