Roysecup,
Thanks for the info - I'd done some research myself and came up with the same answers but I also contacted Royal Precision who informed me this shaft is no longer produced but weren't forthcoming with anymore info. Anyway the set I purchased were more expensive than yours but they were specifically trimmed to suit a set of Callaway X16 Pro Series irons.
Will get them fitted at the end of our season (end September) and get used to their "different characteristics" over the winter. Will keep you posted as to how they perform.
Thanks again for the reply

All the best
Twister