fin-blanks

How to Identify Your Fin Box in 30 Seconds

5 min read· Mr Chill· 03 Jun 2026

Journal Draft — How to Identify Your Fin Box in 30 Seconds

Pillar: Gear

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How to Identify Your Fin Box in 30 Seconds

Buying new fins is the cheapest way to make your board feel new again. But before you pick a colour, you need to know which base fits your board.

Flip your board over and look at the holes (the "boxes"). Here is how to identify yours in about 30 seconds.

1. The Long Centre Box (US Box)

If you have one long rectangular slot in the middle of your board (common on longboards and mid-lengths), that is a US Box.

  • Look for: A sliding brass plate and a small screw.
  • What fits: Any fin labelled US Box.
  • Pro tip: Moving the fin forward makes the board turn tighter; moving it back makes it more stable.

2. The Single Long Slot (Futures-style)

If your side fin boxes are one continuous long slot, you have a Futures-style system.

  • Look for: One screw at the very top (rear) of the box. The fin base is one solid flange that drops into that single slot.
  • What fits: Any fin labelled Futures-style.

3. The Two Small Slots (FCS I-style)

If each fin box looks like two separate small holes or slots, you have an FCS I-style (dual-tab) system.

  • Look for: Two screws (one for each tab). The fin has two distinct tabs that "click" into the two slots.
  • What fits: Any fin labelled FCS I-style.

4. The Tool-Free Version (FCS II)

FCS II boxes look similar to the dual-tab style but are often slightly more aerodynamic and have a larger front slot. They are designed for "click-in" tool-free fins.

  • Can I use Fin Blanks? Our FCS I-style fins are dual-tab fins, not tool-free FCS II fins. They can often fit into FCS II boxes if you use a compatibility infill kit and screws.
  • Recommendation: If you have FCS II boxes and want the Fin Blanks look, send us a photo first and we will check the fit for you.

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Still not sure?

The "Sneaky Photo" method works every time.

Take a clear photo of the bottom of your board (focussing on the fin boxes) and send it to us at bede@finblanks.com. We will tell you exactly what you need within a few hours.

Ready to shop?

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Independent compatibility note: Fin Blanks is independent. FCS and Futures are third-party trademarks used only to describe fin-box compatibility. Fin Blanks is not affiliated with, endorsed by, or sponsored by those brands.