I believe that loose tolerances explain much confusion about this issue. I've seen stems labeled 22.2 that were much closer to, or actually were, 22.0, and the steerer in my Gitane SuperCorsa is also near to 22.2mm. When I decided to replace the Pivo Professional bars/stem on the Gitane with Cinelli (since the original bars on this 60cm bike were only 34cm wide), I selected a 22.2mm Cinelli stem because it required only light/moderate sanding to fit perfectly.
More commonly, a 22.2mm stem will require lengthy, heavy sanding/filing to fit into a normal, say Peugeot, steerer, but this time it was a breeze, and I recall it was both steerer and stem quill in this case that were on the "loose" side of spec.
As for steerer strength, no worries. Only the thickness up where it's threaded should be of much concern, as the lower end is heavily butted. As long as the stem expands below the threads I'd say it's plenty strong, tho many steerers have way more threaded length than is needed.
On a related note, in searching for longer-extension stems for my Schwinn Super-sports, I've found several brands of stems that have 21.1mm quill diameters but which have the same I.D. (bolt hole size) as the similar 22.2mm model (GB, Nitto, SR and Compe) stems. All appeared forged, save maybe for the Nitto Young, but still plenty strong.
David Snyder Auburn, CA usa
Hugh Thornton wrote:
Some bikes with 25mm French-threaded steerers do take 22.2 mm stems, but I have never been sure whether that was because of tolerances in the steerer tube or subsequent reaming or by intent from the factory. I have one such bike and take comfort from the fact that it has a wooden plug up the steerer to reduce the probability of a catastrophic failure. A standard French steerer tube has less wall thickness than a 1" one, and even less with a 22.2 mm hole down the middle.
22.0 mm Cinelli stems appear from time to time on French eBay, but you need to be a bit cautious - one vendor told me a stem was 22.0, but when it arrived I measured it at 22.2. I don't think he was trying to deceive because I asked him the non-leading question of whether it was 22.2 or 22.0. I think there is more chance that the vendor knows what he is talking about if the item description states 22.0.