No, sorry, it's me that I haven't paid full attention to the words of your message, not seeing the clear word "a piece of and old carbon BOOM extension" and incorrectly thinking at a piece of MAST, so that could be only EXTERNAL in my mind.
And also this solve the problem about doing it or buyin' it since I've some pieces of mast but no pieces of carbon boom at all, and no windsurfing friends to give me it. So no photo is necessary, in any case all is clear. And therefore I've already ordered the extension (if they confirm me the discounted price...).
Thanks really a lot for help.