French handle bar stems prior 1980 were generally 22.0mm in diameter.Today's stems have a diameter of 22.2mm. While the purists might prefer to keep those old stems and handle bars, the reality is, they were quite ugly to look at and had the added disadvantage of not being able to take a modern 25.4mm/ 26.0mm clamp area handle bar without a lot of huffing and puffing. The Nitto 'Technomic' is a thing of beauty and with a little bit of elbow grease can easily be converted to French size. In fact,with just a bit of grease, you could force it straight in, but you would have enormous difficulty getting it back out again and most likely damage your forks/ front wheel in the process. Be warned; this is a one way ticket. Once you put the file to the metal, there's no going back. (and there's no taking it back either as the warranty will be voided)
Worm (hose) clamp
Emery paper~various grades
I have been using the long version of the Nitto Technomic. Decide how much of the stem you want emerging from the head set and mark it off. I use a worm clamp to create a nice strait edge and give it that professional touch .
Now start filing. You will be taking 0.1mm off, all the way around.ie 0.2mm from the diameter.Just work your way around and keep filing. Should take about 20 minutes. Use the micrometer to keep an eye on the diameter as you go.
Once you have it down to 20mm try it out for size. You may still have to file some more off.Once it's a good snug fit,I like to finish it off with ever decreasing grades of emery paper to give it a smooth finish. You don't really have to do this as it will be inside the steerer tube but it gives you that warm fuzzy feeling,right? .22.0mm and it's ready to insert. Apply just a whiff of grease all around and insert into the steerer tube,align and tighten the expander bolt.You are now ready to thread in the handle bars. I used Nitto/Velo Orange 'Left Bank'bars as they give the bike that classic French look and are perfect for hanging a basket from. Be extremely careful at this stage as the bars are very easily damaged by the stem clamp. You may need to rotate the bar through 180 degrees as you insert it around the corners.
Ooh La la !