Chains have rubber sealing rings, to keep crap out of the internals (and lube in. O rings are what we're used to seeing all over the place. X rings give 2 points of contact with the surfaces, so in theory a better deal. Z ring, I dunno if they sit upright (to give 1 long seal) or horizontal (to give 2 again) but idea will be a better seal again.
Hadn't heard of z ring, if I'm honest, but that'll be the general idea I think.
Sent from my HTC Desire S using Tapatalk 2