I just bought what I believe is either an Exage or RSX rear hub and it's my first freehub. Going onto what is currently a 6 speed frame, will I have any problems with a 7 speed cassette? From what I've read the freehub has capacity for it and I know the spacing is 126 which is correct for my frame. Basically I lack the understanding of how you can fit an extra cog in the same space with the same width chain (current chain is like new and 3/32 wide.).

Additionally, if anyone could point me towards a 13-26/28 cassette I'd appreciate it. I've seen 14-28 HG online and I might do that rather than paying vintage prices on eBay for UG.

Thanks