Take a close look at your UG freehub body. If one slot for the splines on the cassette is wider than the other slots, it is a UG-HG hybrid body. Also look for threads on the inside lip of the body where a HG lock ring threads into place.
Saving and utilizing the spacers from your 7 speed cassettes and using sprockets from new 8 or 9 speed cassettes is also an option. Just purchase the less expensive models which have a retaining screw or a rivet holding them together. I've even mixed SRAM and Shimano sprockets in the same custom cassette.
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Bob
Enjoying the GA coast all year long!
Thanks for visiting my website:
www.freewheelspa.com