I just purchased an X-ring chain with sprockets for my KX500. I never heard of an X-ring chain, myself, until I looked into these premium chains. The X-ring is an improvement over the O-ring in that the seal is better. If you take a standard O-ring and slice it, the profile looks like an "O". The new X-ring, is a special O-ring in that its profile looks like an "X". This gives a double surface to seal. Kinda like the double and triple edge wiper technology.