BVM Super (Balsa) Bandit
The rod that is used to secure the fin into the fuselage is made up of two parts - a steel outer pipe, and an aluminum inner rod which you must glue inside the steel pipe. Since the aluminum rod is slightly shorter than the pipe, ensure that they match at the bottom .
The rod is held inside the fuselage with a sturdy aluminum bracket that has a grub screw tightened up against the rod. Inside the fin, the rod is secured by not only gluing it to the ribs, but also sandwiching it between a couple of plywood support plates and balsa sticks as is shown below:
You may notice from the photo that the shear webs go up only as far as R4, and also that the R2 <-> R3 shear web leaves a slight gap since it is about 1/8" smaller than the gap between the ribs.