Robin, sorry to be fin-dense, but could you put up a pic of what you are talking about? Many thanks.
Aloha Greg:
If you are talking about the V-notch, attached is a drawing that shows what the notches look like in 3D. I’ll try to take a photo of one to post as well.
The V-notch provides a landing on the fin for the grub screw allowing it to exert downward pressure on the fin that is then also transferred to the insert. Because the insert and the side of the slot in the box are tapered this creates a compression fit as the pressure is applied. Before we had this notch the pressure of the screw would actually push out on the box spreading it, this same problem can happen with FCS fins, although if they are plastic the screws will typically push into the fin creating some downward pressure. This caused the fins to be less stable in the box, with the V-notch and the compression fit the fins are now rock solid.
In reality the notches look a little different when routed as they tend to be round on ends of route. The drawing shows what the notches look like in the molded fins.
