I cut the birdsmouths for the mast extension today, they need a bit of a tidy up but they are not too bad. It always helps to have some scrap stock you can use to get the cut right. I still didn't get it perfect, but I was able to trim a mm or 2 off one side with out affecting the finished diameter. And dry clamped. I don't know why I bought these large hose clamps, but they are the perfect size.