Geoff,
The steerer generally has another tube brazed inside the steerer that sticks above the threads that the stem is clamped to. It works fine.
Brian Baylis
La Mesa, CA
Drooling over Jan Heine's great book The Golden Age of Bicycles I noticed that some of these constructors used clamp on head-stems over threaded fork steerers.Did they strengthen the steerers or was there a high rate of failure at this point ? Clamping a steerer in this way over steerers that I have seen does not seem like a very good idea given the wall thickness left below the root of the thread. Geoff Duke Melbourne Australia