Headset thread confusion

Hi All,

Im new to the forum and also bike fixing/maintenance so looking to learn as much as possible. I have searched the forum and google for the answer to my question but not had any luck working out what I need so any help with the following is much appreciated.

I am in the process of building up a single speed and have an old reynolds 531 frame, it came with two set of forks. The problem i'm having is that the headset lock nut that came with the frame only fits one set. I measured the outer diameter of the thread and one set is 25.4mm and the other is a little larger at 25.8mm. both have an inner diameter of 22.3mm. Can anyone help me identify what I need to fit these forks?

Thanks for your help.

are there any numbers on the locknut that doesn't fit?

sadly not, not even a brand name on it

Thanks for your reply.

can you put up pictures of the various items?

This is a handy reference.

Unless you have an Austrian pair of forks, either your measuring is off or the forks are damaged...

Just use the other forks, no?

^ This
One fork is 24tpi, the other 26 tpi

I foolishly had the pair i wanted to use powder coated black before checking it all assembled. Its odd how the other threaded bit, the adjustable race, fits both pairs of forks. Its just looser on the chrome set, this makes me think the pitch of the thread is the same on each.

So heres the forks i'm having trouble with

And the other set

Thanks for all you help and answers so far!

Looking at your measurements and Sheldon's table, I suggest that you have two pairs of ISO/ITA/JIS/RAL forks, but the black ones were poorly made, hence the deviation from standard.

Measure your crown race to narrow things down.

It sounds as if your HS may be made up from bits & pieces: a Stronglight A9 from Ribble or a Tange Levin from SJS will be £20-odd well spent.