I thought I was buying thicker-walled tubing for the akas (cross-bars) for the new amas, but it turned out I bought the same size. It's 1" diameter, the wall is one-sixteenth of an inch thick. I got two 8' lengths. I replaced the old akas with the new tubing anyway, because the old tubes had quite a few extraneous holes in them, as they had been salvaged from a previous installation.
I started out putting the amas at the ends of the 8'-long akas, but it didn't look right: there was too long a piece of tubing for the size of it, in my mind. So I tried the old akas; too short, the amas too close to the waka (main hull). Decided to add two inches each side, making the akas 7' long. To my mind, it looks to be in a better proportion.
Since I didn't get the thicker-walled tubing I thought I was getting, I'm seriously thinking of filling the (marine/aircraft grade 6061 aluminum) tubes with wood, in order to add strength. Dowels are too heavy, so I'll have to cut them from a plank of some light wood, like pine, and plane corners off. It's better if they don't fit exactly—for instance, if there are flat spots the length of the dowel—as that leaves more room for the epoxy glue to hold the core and skin together.