Got to back Carl up on this one.
I have broken 3 screws also,1 on my iSonic 122 and 2 on my 94. The front K9 inserts should be removed as they only serve to increase the shear force on the screw in hard gybes. I also tighten the screws every session and even take the tiki tool in my back pack to tighten during the session. I also think that the screw finish has less friction(than others i have had) and works its way loose with the continual slight movement of the strap when sailing in chop. This is the only negative of a fantastic range of boards, but can also be the most frustrating as the screws are a pain to remove.
I have made over 10 custom boards and always use 4 screws per strap without any problems. My 94 has inboard inserts to allow this but not the 122. Surely this would be a small weight sacrifice for straps that never twist.