My old bike shop mechanic (and I confirmed with Sheldon Brown) said there's 2 sizes of chains (ignoring single speed & BMX for the moment): 2.30 mm width for 6-7-8 speed, and 2.29 mm for 9-10-11 speed. I'm suspicious that one-hundredth of a millimeter difference in width can matter at all?? Apparently when my chain broke my friend & I put a 9 speed chain on an 8 speed bike. My old mechanic said that could damage my cassette, could 0.01 mm difference really do that?

The chain is rubbing on the rear derailleur and it was when I called to find out what I should adjust, that this came up. He said don't adjust anything right now, just get the right size chain.

Nashbar has completely confused me. It looks like I could get a SRAM chain for $15 +sh which is pretty good, but if I don't want a SRAM chain I have to spend about $30? Is that typical? Should I look somewhere else for a chain? (I'd get it from LBS but that is 90 miles away. Rural living!)

The other thing I find confusing is that Nashbar sells 6/7/8, 7/8, 9, 10, and 11 speed chains. But there are only 2 widths, so what are all these chains?