FCS Longboard Box Adapter

Initially, I ordered a custom mid-length surfboard with a box setup to use a single fin and optional stabilizers. But then I decided to test the Thruster setup, and it ended up working so much better than I expected! The FCS adapter is perfect, it fits seamlessly, performs flawlessly, and I haven’t taken it off my board since. A total game changer!

The fin into the adapter is a tight fit. Some lithium grease helped. The adapter to fin box was tight also, so i took some sand paper and smoothed the sides of the adapter a little, then a bit of grease on it also. Very happy with this. I turned my long board single fin into a thruster setup..

purchased for a surf sup... installed without problem and allow versatility of dropping in my surfboard fcs fins in my surf sup.... great idea, great product, good price. only complaint.... and total disclosure... i own a surf shop and ordered this for myself when we were out of stock.... we have had a problem with these being too deep.... much like some longboard fins we get in... the adapter where it screws tight into the board is sometime thicker than the longboard/sup box.... meaning you can tighten down and still not have pulled tight in box but have tab pulled tight to bottom of adapter.... this leaves adapter or fin felling loose and able to slide... if this happens you need to sand the adapter down to where it's thickness is less than the track in box's thickness... no big deal but it is a problem we have seen and if you know how to fix... then it's not a serious issue only an inconvenience that can be fixed in minutes.

The FCS Box adapter works perfectly with original patented Fins Unlimited US made longboard box. I've read other reviews with problems, likely because their fin boxes are actually Chinese knock offs. The FCS box adapter small "Grub Screws" are designed / positioned to hold the fin securely when the longboard box attachment screw is in front of the fin. It's also critical to tighten the Grub screws evenly and very firmly to ensure the fin stays secure in the adapter. Overall this is a very nice solution to convert to FCS thruster fin setups on Stand Up Paddleboards and Longboard surfboards.

The set screw for the rear tab doesn't lock the fin in it actually pushes the fin tab out of the converter! That would make it very easy to lose a fin. Some FCS fins are very expensive to replace. It would make me very angry to lose one of a $100 set of fins because of this design flaw. I had to drill through the side of the fin converter and my fin to make this work. This should not have been necessary. The rear set screw should be like the front one instead of at an angle. I expected better from a company like FCS. They make great fins but their fin box adapters are crap!

The beauty of having an adapter like this is it allows you more flexibility in fin choices. I tend to go against the grain and believe that smaller fins make for a better riding experience, so not only can you use this adapter to convert a longboard with a single & side-bite configuration to a thruster, which is kind of what it's intended for, but also to take a single fin board and use a small fcs fin to loosen up the tail. If you know how to turn a surfboard you really don't need a lot of drag to accomplish it, and having the freedom to pop it loose and slide a little makes for some fun motion.

Putting it in & out one time destroyed it.

Fitment like others have said is very tight. Had the adapter been 1/2-1" longer for the front screw and plate it would've been perfect. I guess these don't fit XL sized center thruster fins probably meant for everything size L and below. Fits great in the center fin box of my Naish Mana tho. Just a little bit of filing of the base of my FCS HI-1 fin and a redrilled hole an 1/8" forward should be able to give access for the front screw to screw the adapter down. Was hoping it was gonna be a plug and play deal. Modifications obviously necessary in this case.