Campagnolo made lots of different 8-speed freehub bodies, with 3 different spline patterns.
8-Speed
- The first was the pre-Exadrive spline pattern, which came out in 1991. All splines were the same width.
- Next was the ExaDrive spline pattern, which came out in 1994. It was almost the same, but one spline was widened to prevent the cassettes being put in the wrong rotational position on the freehub body. Position was important for Exadrive to allow for smooth gear changes.
- At the very end of 8-speed (1996 from memory), Campag came out with an 8-speed titanium cassette, with a new freehub design.
Notes on 8-speed.
- Exadrive cassettes will work with pre Exadrive hubs.
- Pre Exadrive cassettes will NOT work with ExaDrive hubs, due to the one wider spline.
- 8-speed titanium cassettes are basically composed of thick 9-speed sprockets, and will fit 8-speed titanium freehubs, as well as 9, 10 & 11 speed.
HOT TIP!!!
- My favourite hubs are pre Exadrive hubs. You can use the newer Exadrive cassettes as well as the older 8-speed cassettes, so you know that just about every 8-speed cassette will slide on. The other really clever thing that I don't think anyone has ever realised is that since the spline pattern is reversible, when your cassette wears out, you don't have to chuck it away. you can simply turn the worn out cog(s) around and you effectively have a brand new cassette again. No other cassete allows you to double its working life this way. Sure, you don't get super smooth gear changes, but we're not racing on this stuff anymore, so who cares? There's an awesome money saving tip for you all, but it only works if you have the Pre Exadrive 1991, 1992, 1993 or 1994 hubs.
9-speed
The design was essentially the same as 8-speed titanium. I have never tried but I would expect that 8-speed titanium would be compatible with 9-speed, but with a slightly shorter length to the freehub body, since you only need 8 sprockets.
10-speed
Lighter design with fewer splines, but the same essential spline pattern as 9-speed, meaning that 9 and 10 speed cassettes are interchangeable with 9 and 10 speed freehub bodies.
Some people report that it is possible to get 8-speed cassettes to slide onto the 9/10/11 speed freehub bodies, thereby providing compatibility between 8-speed cassettes and later hubsets. I personally would never try this, even if it is possible to do. 8-speed cassettes had lots of shallow splines, whereas later versions had fewer splines which were much deeper. Mounting an 8-speed cassette on a later freehub body will damage the freehub. Since the freehub bodies are alumium now, and the 8-speed sprockets are steel. With the shallow contact points, the 8-speed cassettes will rip your 9/10/11 speed freehub body to pieces.
11-speed
Pretty much the same as 10-speed. Beyond my field of expertise...
Having said all that, if you have a combination of hubs and cassettes that you want to use, it is usually possible to change the freehub body on the hub to facilitate the desired combination. After you have changed the freehub body, you will probably need to redish the wheel, since the 9/10/11 speed freehubs are wider than the 8-speed ones. If you don't redish the wheel, your rim will be off-centre, and/or the rear derailleur will go into the spokes when using the lowest gear. Campagnolo advises against upgrading the freehub body on 8-speed Shamals because redishing these wheels to the correct position exceeds the maximum spoke tension recommended. Having said that, I have seen plenty of converted 8-speed Shamals and I've never seen a broken spoke on any of them...
This link is a great visual version of some of the info I have given.
I’m feeling I have a pre-Exadrive!?! 
