Sheldon's Wrong! (about Dura Ace 7800 freehub compatibility)

[CrankNFurter]

OK, one tiny mistake... I've learned so much from his website that I won't begrudge one error! But for the record and to assist anyone else out there with 7800 hub compatiblity issues I thought I'd share my experience. There is a supply of stupendously cheap Dura Ace 7800 hubs out there at the moment ($60-90 USD) for front and rear. I was tempted using them for my first ever wheelbuild - fully knowing the compatibility issues.
There is a lot of misinformation out there about these hubs - many posts on many boards warn people that only Dura Ace cassettes will fit. Sheldon himself categorically states that they will fit any Shimano 10 speed cassette. I have found out this is erroneous. The more correct statement is they will fit 10 speed Dura Ace, Ultegra and 105 cassettes only - Tiagra will not fit even if 10 speed. I can personally attest to DA, Ultegra cogs fitting fine, and to Tiagra not fitting - but I have no hands-on experience with 105. However from pictures it certainly looks like they have the tall splines so I think we can trust Sheldon on that one.
An even more correct statement would qualify that only positions 3-10 actually have the tall splines, so effectively 1st & 2nd position cogs from any Shimano-freehub-compatible sprocket can be fitted in the outboard positions.
Apparently 7801 freehubs share the features of 7800 but I warn you that I haven't handled these personally so can't guarantee the above applies to 7801's. To summarise, FH-7800 can fit CS-7800, CS-7900, CS-6600, CS-6700, CS-5600, CS-5700 cassettes.

[Thoglette]

The more correct statement is they will fit 10 speed Dura Ace, Ultegra and 105 cassettes only

Which is what Sheldon says in the two references I can find.
https://sheldonbrown.com/k7.html#aluminum

From 2004 through 2007, Shimano used aluminum bodies for the Dura-Ace 10-speed model. To avoid this problem, Shimano changed the spline pattern, making the aluminum spline ridges significantly taller for better support. The downside of this is that those hubs will accept only Shimano Dura-Ace, Ultegra and 105 10-speed cassettes.

https://sheldonbrown.com/dura-ace.html#10

As a result, it is not possible to install cassettes other than 10-speed models on Dura-Ace 7800 hubs. It is not, however necessary to use Dura-Ace 10 speed cassettes. The Ultegra 10 speed cassettes also accommodate the taller splines of the 7800 hubs.

Where's the incorrect statement you refer to? I'm sure the curators will want to fix it.

Note that Tiaga only got 10sp in 2011, some three years after Sheldon passed away. So we should possibly be blaming Jobst Brant or John Allen.

[Duck!]

The offending passage may have ben written before 10-sp. Tiagra was introduced, and overlooked in subsequent edits. There may be some third-party compatible cassettes (I believe SunRace manufacture a deep-spline cassette range), but as a general rule only Dura-Ace, Ultegra and 105 10-sp. will fit on the dedicated 10-sp. body.

The 7801 updated model (and related 7810 & 7850 wheelsets) uses a titanium freewheel body, which reverts to the standard shallow spline, as well as being 1mm longer than the dedicated 10-sp. model, so will therefore also fit 8, 9 and other 10-sp. cassettes; said 10-sp. cassettes therefore require the 1mm spacer not needed on the dedicated 10-sp. hub.

[CrankNFurter]

Thank you for your replies - I guess the above explanation is correct about Tiagra 10 speed coming out after the website was archived. BTW I'm very grateful to people like Sheldon and Jobst, didnt mean to imply any disrespect - only to save some money for those out these heading in the same direction.