This is a fin model for the US Box. There are two models, one thin and one thick. Pictured is blue and green. It's best to make the pin for securing it to the base of the SUP out of metal, drill a hole, and insert it into the fin base with a tight fit. The blue one in the photo is thin and made of PETG. It's been used for several seasons and, as you can see from the photo, has already broken (ive another on that has broken 5 times). The good news is that PETG glues well with super glue and retains almost no strength. However, it's generally fragile, especially in cold water. My next green fin is thick, printed from ABS, but hasn't been tested yet.

I would recommend not printing the holes for the mounting bolt; drill them in the already glued fin.

Regarding the fin gluing process, I recommend gluing the front and back first, then the right and left parts. Because the parts are printed in different positions, their axial shrinkage varies, and you may need to adjust their relative positions.