Originally Posted by
jonwvara
Another question remains unanswered, though: As SquidPuppet noted in that earlier thread, some people get really exercised at any suggestion that it's safe/reasonable to thread a threadless steerer. Casual measurement seems to suggest that both the OD and wall thickesses of the two are the same, but I still have some lingering doubts. Andrew Muzi at Yellow Jersey told me that you can in fact thread a threadless steerer, but that the diameter is slightly too small to get an ideal thread; he implied that the difference might be on the order of a few thousandths.
To add a data point, some years back I had a new frameset with a threadless 1" fork and decided to have the fork threaded so that I could use a traditional quill stem. I found a frame builder to do that, and all was good, but, darn, that steerer was way tight for a 22.2 stem. I managed to get one in, but it took a lot of force. Yeah, I should have tried a French/22.0 stem.