backstory: I'm building up a late '90s Bianchi Trofeo (I think) frameset for a co-worker to use on the Aids Ride.
I told her I had a nice pair of wheels with Campy hubs and the 8-S cassette to go on the rear (this would come off a rear with a tubular rim that has no tire and so is a spare).
So...I find the wheels. Nice indeed with Mavic OpenPro rims and Chorus hubs...pull the cassette off the other Chorus hub and slide the cogs on the new hub. Now just screw that lockring on and...no...it will... not... fit...
The old Chorus body uses a lockring with a 29 MM threaded OD, the new one looks like it takes a 26mm OD.
What gives?
Didn't Campy standardize these things?!? (and I thought Shimano was bad!)
help me out, I can't find the info in the catalogs, don't even know the exact years of the hubs involved...what lockring do I need to make this work?

The lockring size depends on the size of the smallest cog on those Campy.
The cassettes that have 11t , for example, would have a smaller lockring than those with a 13t smallest cog.
There is a tooth count where the size of the lockring changes. I can't remember if it's 12t or 13t, but that appears to be the issue.

OK, Thanks for the reply, but in this case the cassette/small cog is the same size and transfers between the 2 bodies with no hitch, so I'm a little confused. The old body is black finish and seems to have straight-sided slots or grooves for the cogs, the new one is silver (could even be alloy) and some of the slots are undercut, but the cogs still slide on anyway (thanks, Campy, for at least that much interchange). So...

Guess I'm ISO a small size lockring for a Chorus hub of unknown year. Will trade...PM me.

BTW, Robbie, I might be keeping the BB with the horrid divot cups for this project, but then again...if I can't make it all work with Campy parts I'll scrap this approach and go to "Plan S": all Shimano or S-compatible drivetrain. She'll just have to cope!

If the smallest cog is the same size, the lockring should be the same size, unless the cog was originally on a 9-sp cassette.

If you're transfering the same cassette from one body to another, then one of those bodies is for an 8, one is for a 9, I believe.

I'm fervently hoping someone can help here. I may ask Spinz, as I know he's got experience with both. I've got a couple Campy BB's but they are Italian thread....let me know if I can help.

Someone at Branford Bike would probably know: https://branfordbike.com/articles/cas...-cogs-pg60.htm

I have vague memories of a similar problem. I think the small cog size requires a different sized flange. You're talking about the thread diameter. So, you can have different thread diameters and different flange diameters.

Sounds like it might be an 8 speed titanium body? But it's confusing the lockring won't transfer.

Here's what I found out (so far) and it's probably not the last word:
The lockrings come in 3 sizes of thread OD:26mm, 27mm and 29mm
The old 8-spd. body I took the cassette from used the 29mm ring and was probably from around '91 to '94.
the NEW body/hub might be a 9-spd but it was sold to me as an 8-spd and the 8-spd cassette fits on perfectly (at least until I do the last step and see if a lockring cinches it tight). This hub is marked Chorus and has to be a '97 or '98, it takes the 26mm ring ('99 Athenas are the other hub/year that used 26).
All the later rings (Campy and Miche) seem to be 27mm, but there are 2 sizes of flange (what I mistakenly was calling the thread OD) that match either a 11t or a 12t small cog.
So...
I'm looking for a Campy lockring with 26mm thread OD and will swap a Campy sealed BB unit for one...I'll post this in ISO and a pic of the BB, too.

I've got 3 spare 29mm lockrings. That's all I can find.

JYB, thanks for trying!
I've updated my ISO/trade post with corrected info and pics, it's post #3148
here's pix of the BB just for grins