Thanks - someone else told me about that last night as well and I found that article by Zinn. This was on a Mavic freehub which is one of those noted in the article that can be mounted incorrectly. I had no idea. Been riding Campy on all my road bikes for over 10 years on various hubs and I always thought they would only go on one way. Going to look at those pics and check the rest of the cassette tonight. Although no way I'll ever know on the one that broke as it is in two pieces on the road somewhere....