This is a bit esoteric, but may be important to some folks: There is more than one "standard" for lock ring threading for fixed gear hubs. I was trying to fit a lock ring to an "FB" (Italian) hub this morning, and the first rings I tried just wouldn't fit. So, using the hubs available, I did a bit of measuring. Sure enough, I got the following results (where I'm using lines of dashes to let you know where the line breaks are, since this can get messy with email):
F.B. (Italian): 1.313" (33.4 mm) ----------------------------------------- Harden (G.B.) 1.290" (32.75 mm) ------------------------------------------ Paramount (US) 1.305" (33.2 mm)
The Paramount hub barrel has been rechromed, so I suspect it is the same as the Harden, and that this is a "British Standard." I did not check the thread gauge, since threading on seemed no worse than class B (will work, but doesn't feel perfect).
The one lockring I found that did fit the FB was real loose on the Harden (sort of like a 14 mm pedal in a 9/16" hole). If you find such loose fits, I would not recommend using them if you count on the lock ring for braking.
I don't have a Campy track hub to check. There was no info in Sutherland 2nd Ed, the only one I have.
Your mileage may vary...
harvey sachs
mcLean va