For years I'd thought you used a narrower chain as you go to higher cog counts (since 7- and 8-speed HG clusters are spaced more closely than 6-speeds or APII 7-speeds, and 9- and 10-speeds are said to be tighter still), but now I've come under the impression that ALL derailer systems use a chain that's 3/32" wide! Of course, there are lots of different chains specifically marketed for different cog-count shifting systems ... if they're not different in width, what IS the difference?