Three systems. You need to know which one your board uses before you order anything. That's the whole point of this post.
We'll keep it short.
US Box
The original. A long slot — usually 10 to 11 inches — routed into the board. The fin slides in on a base plate and is held in place by a single bolt through a nut that lives inside the box. You can adjust how far forward or back the fin sits, which changes the feel of the board. Move it forward: looser, easier to pivot. Move it back: more drive, more tracking.
US Box is the dominant system for longboards. If you're riding a noserider, a performance log, a mid-length with a single fin, or anything over about eight feet, there's a very good chance it has a US Box. Shortboards rarely use it.
Our Longboard | Resin | US Box range is designed for this system. Hardware included.
Futures
Futures uses two tabs moulded into the base of the fin that slot into two fixed boxes glassed into the board. The fin clicks in and is secured with a grub screw. No movement forward or back — the fin position is set when the boxes go in during the shaping process.
You'll see Futures on most modern shortboards, performance twins, fish, and mid-lengths from the last fifteen or so years. It's a clean system: simple to use, very solid once locked in. The downside is that you can't adjust position, and the tab geometry is specific — a Futures fin won't fit an FCS I box.
Our Twin Fins | Resin | Futures and Keel Fins | Resin | Futures are made for this system.
FCS I
FCS was the first widely adopted fin system for shortboards, launched in the early nineties. It uses two small cylindrical plugs glassed into the board, and fins lock in via a matching two-hole base with a grub screw holding each plug. You'll see it described as "FCS" or "FCS I" — same thing.
A huge number of boards from the mid-nineties through to about 2015 use FCS I. If you've inherited a board, found something secondhand, or are riding anything from that era, check the fin boxes: two separate cylindrical holes, about an inch and a half in diameter, positioned at an angle. That's FCS I.
Our Twin Fins | Resin | FCS I fit this system. They do not fit FCS II (see below).
FCS II — the short version
FCS II launched around 2013. It's a click-in system — no screws. The boxes are a different shape, and FCS I fins don't fit FCS II boxes without an adaptor. FCS makes FCS-to-FCSII adaptors. We don't currently make FCS II fins, so if your board uses FCS II, you'll need to either use the adaptor with our FCS I range or wait until we expand into that system.
How to tell which system your board uses
Pull your fins out and look at the base of the fin. Then look into the box on your board.
- Long slot, about 10 inches, one bolt: US Box
- Two rectangular slots, parallel to each other, each about 1.5 inches long: Futures
- Two cylindrical holes, about 1.5 inches in diameter, angled toward each other: FCS I
- Two rectangular slots with a rounded end and a notch: FCS II
If you're still not sure, photograph the box and email us. We'll tell you what you've got.
Does the system affect the feel?
The system affects how the fin is held — not how it performs. The fin template, depth, rake, and foil are what shape the feel. Two fins with identical templates, one Futures and one FCS I, will feel the same in the water. The box just holds them there.
The one real-world exception: US Box fins can be repositioned, which does change feel. That's worth experimenting with, especially on longboards. Move the fin 10-15mm toward the tail and the board will pivot more freely. Move it forward and it tracks harder.
For more on how fin shape affects feel, the Try Something Weird guide covers the basics — rake, foil, base length, and what each one does.
Three systems. Check your boxes. Order the right one. That's it.