Originally Posted by
jonwvara
Another question remains unanswered, though: As has been discussed in other threads, some people get really upset at the 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.
I don't have a selection of threaded and threadless forks handy to measure. Is there someone with an accurate digital micrometer and a stash of assorted threadless and threaded forks who would be willing to take some measurements and post them here? It would be nice to either confirm that bit of folklore (that threadless steerers are ever-so-slightly-smaller-dimensioned than threaded ones), or knock it on the head for good.
I ride a 51cm, so when I came across an SR Prism fork out of a 60cm frame I was able to simply cut off the threaded section and use the fork with a threadless headset.
If Muzi is right that there are dimensional differences in the steerers, it certainly wasn't enough to prevent my CK headset from fitting and adjusting perfectly.
My threaded Fuji steel steerer is 1.000", my Bianchi threadless is .997" and my Kestrel EMS threaded is .998'. This would suggest there is more variation just in the threaded steerers than between threaded and unthreaded.