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Yes, but it's not an easy job. There's a fair bit of metal to be removed, and that's hard work with a tapping die. Fork threads are normally cut on a lathe, but once the fork is built that's not really an option. Also, it's critical that the die is straight when it starts to cut the thread, otherwise the thread will go off-centre and weaken one side of the fork. It's not a job I'd want to do myself, but you may find someone out there who has the tools, skill and brute force to be able to do it.
Brommers-
Ah didn't think of it that way. I thought one would just take thread cutter and go for it. Maybe I should look at getting a custom ahead stem instead.
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Yes...
That probably needs some justification.
Internal diameter is of no consequence when designing/speccing a threadless steerer so a quill stem may not fit.
A lot of steel 1 1/8" threadless steerers have an id of 1" so could accept a 25.4mm quill but the p2 fork I'm working on for a forumenger right now was 23.something millimetre and I found another fork in my collection that was slightly larger that.
I suspect 1" threadless steerers will be similarly inconsistent.
Oddo
M_V
For the frame builders and tube connaisseurs. Can you convert a 1" ahead to quill stem by threading the fork and replacing the headset?