These are standard size fins for a shortboard in thruster configuration (3 fins). These fins are made to be compatible with fin boxes made by ProBox. But they can easily be made compatible with FCS fin boxes by cutting a notch in the tab at the base, or glassed on if the tab is fully removed. UPDATE Added a crude futures compatible base. Be aware that Futures side fins have cant built into the fin rather than into the base like FCS and ProBox.
If you like these checkout mesheldrake's Cardboard Surfboard http://www.thingiverse.com/thing:4764 or his other boards at http://sheldrake.net/cardboards/
His most excellent work on these cardboard surfboards inspired this creation.
Also check out my Longboard trailer fin at thingiverse.com/thing:12496
and my longboard side bites at thingiverse.com/thing:12497
If you surf you should be able to figure it out, but here are some instructions for the rest of you.
For side fins use 1/4" or 6mm stock and cut one for each side, flat side faces in toward the center of the board. For the center trailing fin use 1/8" or 3mm stock and cut one of each then glue them together. Set red to vector cut and black to raster. The foil will be made by the black raster, so run it at full power and very slow. I used a 60 Watt Universal laser cutter with power at 100%, speed at 1.5%, and 1000 ppi for 1/4" birch plywood. With a little sanding and maybe some epoxy or polyester resin you can make and surf your own fins.