Pics? ... Is that this?

http://www.amazon.com/Surly-Stainles.../dp/B0016L9FLM

The protrusion inserts under the cog to allow the lockring to have more lockring threads (as opposed to cog threads) to grip on. But note you do not need to use this protruded side, you can opt for the flat side as the protrusion may not be necessary (or on rare case, incompatible as the protrusion make the lockring incapable of ... locking).

Oh and another thing. Don't abusive with it. You can leave embarrassing scratches on the ring with the lockring tool. I screwed up and left huge indentations on the divets. My scared-up Surly lockring works perfectly but clearly display my noob-ness. Heh.