My chain says "Z KMC 3C-2 RB" which I suppose refers to as 'Z8 RB 1/2" x 3/32"'?
The bike shop where I have bought from until now doesn't have this exact model. So what are the key properties of the chain, so I ca buy another brand?
I want to get the best possible quality if possible.
Update
It is a 7 speed.
Update:
Based on your other question: Possible to identify sprocket without taking the bike apart? - you have a Nexus internally geared hub, which would mean you may need a single speed chain.
For derailleur gear equipped bicycles you just need to get a chain compatible with the number of gears ('speeds') on the rear sprocket cassette. More gears require a chain with a narrower outer width because the sprockets are closer together.
Generally speaking derailleur chains are available in 6, 7 and 8 speeds; 9 speeds; 10 speeds and 11 speeds.
Just for completeness and to address the 1/2" x 3/32" measurements on your current chain:
All bicycle chains have 0.5 inch pitch (distance between center of the pins)
All chains for derailleur gear equipped bicycles measure 3⁄32 inch between the inner plates. (Single speed chains use a wider 1⁄8 inch inner width.)
"I want to get the best possible quality if possible." All 1/8" or 3/32" wide chains will work and last about equally-well. Take the mass market leader, KMC, and its mainstay single speed chain. Very inexpensive and in a wide range of colors
The lasting quality of a singlespeed chain is not likely to vary much by make because for practical manufacturing purposes chains are made of more or less soft steel. The silica dust that swirls into the chain incorporates with the lubricant to make a fine lapping compound. Soft steel will lap away somewhat faster than hardened steel. Oil a new chain. Run it a short while. Wipe. The gray color on the rag is the color of wear particles of steel.
The wear results in chain "stretch" entirely at the rivets and the inner plates that flex on the rivets. The rollers wear on their bushings, too, but do not contribute to chain stretch at all. That is, the only degradation which matters is the wear of the rivets and side plates because that ever-increasing slop alters the pitch of the chain. Side plates can be hardened, sure, but rivets, less-so, because then they cannot be riveted very well. And running in the presence of fine silica grit these small and highly pressured parts will grind-away regardless of their relative hardness.
Point: for six dollars, a new basic quality KMC chain is easy to swap in and it has the easiest to apply and remove master link around. Z chain is liable to last as well as any more expensive chain you may buy.
7 speed is enough information. All bicycle chains share the 1/2 inch pitch (with one extremely rare exception) and derailleur chains for same number of speeds are very close to same width.
