Tom -
I've never seen a Mavic SSC headset that looked quite like that one either. I'm staring at a Mavic SSC top-nut (the only piece I have left from this particular headset) and while it looks similar, it is different in several ways. The one I have is keyed for the same tool, but the bevel at the top is much shallower, and the lip above the bevel is wider and printed with "Mavic" and "SSC" opposite each other. On mine, the faces between the slots have a very slight facet, rather than being straight (as on the eBay version). Mine has a very distinct internal shoulder below the top lip that creates a groove for an o-ring. On the eBay version, there may be a groove above the thread-line that holds an o-ring, but on mine there is much more of a space between the thread-line and the o-ring lip, which is very pronounced and obvious. And mine is anodized, of course.
I would tend to support your "prototype" theory. Interesting.
Wayne Bingham Lovettsville VA USA
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There is a French threaded Mavic headset up on Ebay, ending soon. It
looks quite different from the examples sof this style of Mavic headset
that I have seen previously. Apparently, it is all alloy, with no
pressed in steel race inserts. How could this possibly last? Might it
be a "for show only" prototype cranked out for a bike show, before
production was really begun? It also seems to be unused, but quite
corroded, which suggests that it may not have been anodized. All the
examples I've seen were very nicely anodized. In fact, almost every
Mavic part I can recall seeing was anodized, other than a few hubs.
The lack of anodizing makes me wonder if it was not regular production.
Finally, I'll speculate that if Mavic were going to do a pre-production
prototype, it would be in the domestic thread spec.
140111336812
Tom Dalton