I have a wheel with an "Exage FH-HG50" hub (one of these: http://velobase.com/ViewComponent.as...cf2e0&Enum=110).

It has a 7-speed freehub body and hyperglide cassette. I want to replace the freehub body but I'm not sure how to identify a model that's compatible (as I can't find anything for sale which directly refers to FH-HG50, and this is a pretty old bike).

I found this shimano compatibility chart but I don't know how to use it in practice (eg what are the C and S columns?):


Can anyone offer advice?