Originally Posted by taras0000

Typically, any lockring will do, but it depends on which hub you have, not which cog you have, as it is the hub that accepts the lockring, not the cog. Most hubs use the ISO standard, but there are some out there that use separate standards.

33.5 mm × 24 TPI Campagnolo, Gipiemme, Phil Wood, Miche
1.29" × 24 TPI Shimano, Suntour, Formula, Dimension, Suzue, Surly, Zipp, Corima - This is the ISO standard.
33.0 mm × 1 Mavic

There is one case where the lockring/cog combo matters, and that is when you use a 12 tooth cog. They come with their own special lockrings that have a smaller outer diameter, so that the chain doesn't ride on the lockring instead of the cog. I have only ever seen this combination use the ISO standard.