I've just bought one as well and can't find any info on it either.
The clamp bolts are 6/4 titanium and the sleeve is 'Delrin'. It's certainly a nicely machined thing, if a bit heavy..
I don't think they made them for very long, in the mid 90's (?).
-and it came as standard on a top titanium Raleigh in about '96/'97