I just tried to put the ONE Race Ace fin from my wife's 2013 Fanatic Falcon 12'6" into the fin box in my Jimmy Lewis M14. There was absolutely no way it was going in. It was too thick. I would have to thin the base of the ONE fin down by at least 1mm I think. Are there two different specs of fin box at play here?

I've often wondered the same thing.

My mal has a box that is inserted into the board but my SUPs seem to have the box routed out of the board and then coated with some black stuff. I have one fin that doesn't fit the SUPs very well because its too wide.

Its almost like they routed it too narrow.

I noticed the same thing with the base plate for the fin screw. I had to mix and match screws and base plates to find ones that fit the SUP as the channel was too narrow for the base plates but it was too deep for the short screw.

Made it all a bit difficult to get right.

The Mal and the other SUP are fine for all fins.

There is one standard now (actually, there has been some time a deeper version on some sailboards), but:
- some are not manufactured to very stringent specs (dimensions can vary between each box of the same batch)
and, obviously they can vary a lot between manufacturers
- the way they are glassed in can put more or less pressure on the sides and change them a little


In a nutshell this fin box standard is an horrible design, and should have been replaced by something better years ago (for instance with conical walls to eliminate any fitting problems). But for now, just know that having to adapt the fin to the box is unavoidable (except for the new "balls on springs" FCS system on the "dolphin" fin line)

fin boxes vary from brand to brand. US seem to have a different SPEC or something. starboard boxes are deeper. most other fins you have to pack to make them fit.

starby and futures fins sometimes you have to ground off some of the fitting depth to get them in most other boxes.


so i don't believe there is a standard box atm

there are 7 "standard" US fin boxes in boards in my shed. they are all slightly different from each other, enough to be a PITA.

The problem with the boards produced in Thailand (and that is the majority of the productionboards) is that they don,t use original boxxes but a cheaper lookalikes with more variation.For those who need to make there fins thicker: alu tapes works great for that but you can also very easy use 1 second glue to glue a couple of thin strokes glass on the base and sand it down till you got a perfect fit. works almost as goog as epoxi but saves you a lot of time when you wanna hit the water quick.

The majority of surf fin brands we tested before making our US box for inflatable SUP were 8.7mm , there are some 8.4 and a few 9mm

some plastic fins from a **** mold can be badly bowed - which is a main reason we just recently made our own fins too


Some SUP factories get a plastic fin and gloss coat it (to make it look like fiberglass) so the box they're using could be a lot wider than most other fins .

my M14 also has a really tight fin box too, i sanded down the fin to fit.