I picked up a cheap wheel over the weekend that I plan on using for commuting/touring. It has a 7-speed cassette (not freewheel) and after doing a little research I figured out it's an older Uniglide, the kind that uses the small cog as the lockring. The range is 12-21, and I think I'd like something a little wider like a 12-25. I figure I'll be more successful finding something if I was going to go with a hyperglide 7-speed cassette. My question. What's the model # and where's a good source for the Hyperglide freehub I would need to replace the Uniglide one on the wheel? I'm looking to do this as economically as possible. Thanks.

Loosescrews has UG cogs and cassettes in stock.

https://www.loosescrews.com/index.cgi...d=975260516139

There's a chance that you have a Uniglide-compatible Hyperglide hub. Here's Sheldon with everything you could want to know about these hubs and cassettes:
https://www.sheldonbrown.com/k7.html

Also, while perhaps a downgrade, 6 sp uniglide cassettes are still in fairly good supply on ebay, not to mention the site OFG posted. You should be able to find a range that works for you in 6 almost as well as it would in 7.

You can use 6 speed cogs on a 7 speed, except for the second position, which has a built in spacer.

I had read Sheldon's article but not as closely as I should have. Now I'm curious - gotta unscrew that sucker and see if there's a wide spline or not. Either way, doesn't sound like filing down the wide tab on some hyperglide cogs would be that big a deal.

Anyone know if the 7-speed cogs are a specific width (compared to 8's or?) or is the crucial thing the width of the spacers? Do I HAVE to use 7-speed Hyperglide cogs, and if they're sitting loose in a bin somewhere, how do I tell if they are the right width?

Nope, 6-7-8 all the same width, slightly dif spacers, but not nearly as fussy as 10 speed!

If you need different cogs to build your cassette or you want a HG freehub body go to citybikes on 19th.
I built a few cassettes there for really cheap.

I've bought a couple of the HG freehub units on eBay, for around $27 IIRC. There is a compatibility issue having to do with the drive-side axle cone, I think, when trying to replace a Uniglide -- read Sheldon's info carefully. That said, if your freehub is mechanically OK, the use of some HG cogs to augment what you have on there already might work out fine, and be the shortest path to what you want.

Oh man, am I getting an education. I thought my six speed cassette was valuable, but the 7 speed, hyperglide freehubs were worthless. Ooops!

Note that you cannot swap to a 7sp HG freehub if the hub is Dura-Ace.

You don't need to take the cassette off to see if it's HG compatible. Just look for the internal HG threading on the end of the freehub (or a HG lockring that's already threaded in )

6sp and 7sp cogs are the same width (1.85mm). 8sp are just a bit thinner (1.8mm) but the difference is so small that they can be interchanged with 6/7sp.

A few years ago I bought a NOS HG-20 7sp HG hub on eBay and converted my 7sp UG wheel to HG. I swapped the drive side cone along with the freehub although I think the original cone would have worked OK.