I bought a nice-looking set of Alex ACE19 wheels on CL, with nice Formula hubs.
The seller said they were from a Specialized XC bike. Ok, so the colors were right, etc.
He said it was a Shimano 8/9/10 freehub.

I cleaned 'em up and tried to put a cassette on the freehub. No deal.
The cassette will go on about 1 cm or so, to the flange pictured, then no farther.
The hub flanges look exactly the same, they are just about 1mm "thicker" and are in line w/the first cm or so, which fits a Shimano cassette perfectly. There are no burrs or anything on it.

2 LBS's have not seen this type. They tried SRAM, Shimano, and Campy cassettes. No deal.
One older wrench thought it might be a Suntour, but this appears to be later than that.

Here are the pics, and if anyone knows a solution, be it a cassette, or freehub swap, I'd love to know.
Thanks.

First instinct for me would be freehub swap. This will make replacing parts down the road so much easier. I think the main reason for the design above is to use a smaller tooth cog on the small end, but the problem is that if you want to ever use standard shimano or SRAM parts (which that definately is not) you will have a hard time.

Are there certain flanges on the hub that look smaller or larger? Specifically, is there a fat one followed by a thinner one? If so, then a standard Shimano or SRAM cassette should work

10 speed specific Shimano hub. Try a 10sp cassette.

What he ^ said...

From: https://www.ritcheylogic.com/faqs.phtml

You'd think 2 LBS and the owner of a new Kestrel with 10-sp DA would have recognized that.

I haven't had a 10 speed only hub... but they are pretty rare. They came out briefly (like a year or two, and then reverted back to the old style.

I think it was basically abandoned once 105 moved to 10 speed, as it was a Dura-Ace/Ultegra 10 speed thing... I seem to remember reading on Sheldon Brown's site about how to file non-DA cassettes for use on DA wheels...

I am surprised the two LBSes didn't catch it either, so I am surprised that this is what you have.

The 10-speed only Shimano freehub bodies were 7800 Dura Ace hubs and both Dura Ace and Ultegra-level prebuilt wheels. The 10-speed Ultegra and 105 hubs were always 8/9/10-speed compatible.

Shimano did this so they could offer an aluminum freehub body without having the splines damaged by the cassette cogs. The newer 8/9/10-speed Dura Ace has gone back to a titanium body and the shorter splines.

Thanks. I liked the strength of the wheel (36h) and a slightly wider rim for a steel Ironman century bike. I learned a lot from you guys, and rechecked the CL post, he advertised it as a 9/10 hub. He also works/worked at a bike shop....I believe I've been slightly bamboozled ,..but it's all good. If he wasn't an hour away, maybe I'd see if he'd swap out the freehub. I'll see if I can do it...

I don't think an aluminum freehub can be swapped for a steel or titanium one. They attach to the hub body in a different way (at least Shimano's do).

Here is an exploded view of one of the aluminum freehubs (7800)...
https://techdocs.shimano.com/media/te...9830608915.pdf

While here is an exploded view of the 7700...
https://techdocs.shimano.com/media/te...9830610236.pdf