Not sure ?

Have you tried the interweb? I hear there are some sites on it, tho' some are better than others... So I've heard

Only guessing but I'd think you can't use much extension in addition to using the X-tender, as you are changing the bend curve a lot and introducing two points of wobbliness. So the 42cm will not allow you to add 60cm to a mast, it just helps out people who only have a base with no extension.
IMHO

gregob said..
Yep and even the NP site doesn't specify would you believe!!! Answer is probably obvious but I thought i would try and see if someone knowledgeable on subject could clarify...........

Have you sent an email to NP? They are pretty quick to repsond to questions. A couple of years ago I had a questions about sails and mast compatibility and got a respons from Robert Stroj directly with in 24 hrs.

Almost positive they're just for sdm masts. However other brands like north do and rdm option if you're keen for that.
I've used these extensively over the years in formula style rigs so can say for sure they are up to the job for raising a 430 to do 460 work.
Downside is that they obviously change the diameter of mast at boom connection and cam contact points but nothing too bad.
Sam.