Mmmm, Challenger tip (or better said TOP extension) is out of stock and I think they will not produce it anymore.
I've found on Nautix website a similar top mast extension, 30 cm for 22 mm (inside) diameter mast would fit perfectly in the tip of my mast, even if extensions should be used for rdm masts, but tips aren't the same in sdm/rdm? And therefore my special 460/30 seems for thickness a giant fat rdm!
I've sent a info request to Nautix but at the moment no reply.
Someone knows some other brand who still sells mast top extension?