X8 (formerly X8.99): stretch-proof, chamfered plate, full-nickel plated chain for 5-8 speed and great for internal geared hubs Z8.1 silver/gray (formally Z72): chamfered inner plates with Bulls-eye rivets for 5-8 speed Z8.1 gray (formally Z51): standard bushing-less, chamfered plate chain for 5-8 speed Z30: economy bushing-less chain for 5-8 speed Z7: high pin power with reinforced durability and quieter riding experience, smoother shifting