1 inch threaded head-set doesn't screw on the fork


Senior Retro Guru
I have recently purchased an American Classic 1" headset which i intend to use on an AMP fork (1 inch threaded as well). Today I received the headset and when I was messing about with it i noticed that it will only screw on the fork maybe 2 turns after which it will get tight quick, so i naturally thought maybe my threads are kinda dirty or buggered, no need to ruin the nice headset so I dug out an old Shimano 1" top-nut which threads on without any problems whatsoever... hmmm... then I dug out an old Ritchey 1" headset and the top nuts on this one also thread onto the fork without any issues. So I contacted the seller and he told me this headset was on a '92 Specialized S-works with rigid fork. Can anybody here shed some light on this? Is it possible that the Specialized used Italian or French threads instead of ISO threads?


Retrobike Rider
Is it one of those round-topped TriLock things?

Screenshot 2021-04-20 152028.jpg

IIRC you need to make sure that all 3 caphead screws are wound right out, so the top section can float a little, or the threads can be tight.
They pull the top section down towards the lower half and grip the thread...

Maybe split the top into its 2 components and see if either screws on nicely on its own?

All the best,


Senior Retro Guru
Yes it is indeed the round top tri-lock thing. The first thing I did was take the assembly apart and try to screw them on by themselves, with no luck. The main question is still... could the fork on a Specialized S-works be Italian threaded(the fork is original to the frame)? As far as I know they're both 24 tpi but ISO is at 60 degrees angle whereas Italian is at 55 degrees which would explain why I can thread them on 2 turns but then it gets really tight. Any S-works experts out there?


Retro Guru
In an attempt to save your sanity.... if the other nuts fit the forks, then we agree its the headset to blame. Although, i assume your shimano headset was iso not jis as the thread is slightly different.

Taking it was iso....

So either, its an odd pitch (like a Raleigh) or odd angle ( like old campag etc) or its jis or the thread is shot.

To rule out the thread being shot once and for all (and assuming you dont have a tap that size!) Have you tried tracing them round with a pointed metal scribe or angled pick, just to make sure they are not crossed at some point or obstructed by a litte bit of swarf.


Karma King
Only to add a couple of things which might be helpful... I'm fairly certain AC only made their headset in 'standard' format, so unlikely it has different threading to your forks. Second, the AC is an all aluminium headset, whereas the other two you've tried are possibly steel versions? If they're old, they will likely have 'slackened' a little through use which would help them to fit easily - if the AC has only been fitted once [say] and a combination of it being softer aluminium, it might simply need a little more persuasion. Also, the tolerances are very high on the AC headsets [like they are on Royce BBs] so it would probably be helpful to run a die down your steerer just to clear out any gunk - even minimal amounts can have a big impact on quality components like this, over and above more 'regular' fare.