Surfboard Fin Basics 1: Which Fin System

The information out there about choosing the right set of surfboard fins for your size, riding style and waves can be a bit overwhelming for the new surfer, before you can make the decision on the style of surfboard fins to buy you'll have to know some basics that aren't always obvious when you're starting out.

Types of Fin Box

You'll need to know what fin system your surfboard uses before starting to choose your fin, this blog post will focus on figuring out which fin system you have on your board and what you need to make sure you can get a set of fins to match.

Usually you can tell fairly quickly what type of surfboard fins you need by looking at the bottom of your surfboard, you may see anywhere from one to five fin plugs on your board, generally boards with five fin plugs are designed to be ridden with three or four fins at a time with the spare fin plugs left empty.


FCS's latest fin system is much easier to use thanks to it's keyless, Clip-in technology.

Not only does this system allow you to change your fins in seconds (As explained below) but it also creates a flush leading edge for a smooth glide through the water and uses honeycomb plug construction to reduce weight.

If your new board has the FCSII system and you only have your old FCS fins they have handily made a Tab infill kit allowing them to fit.

FCS Fin Plugs

Each FCS surfboard fin is attached by inserting two tabs, around an inch long, into two slots in the bottom of the surfboard, the slots at the rail have small holes on the inside edge which allow a small grub screw to be screwed in and secure the fin in place, the slots in the middle have one screw hole on the right and one on the left.

All these FCS Surfboard Fin plugs accept the same FCS fins, the top of the deck sometimes has stickers to cover the circles of resin

There are a few types of official FCS plugs that you may encounter, the FCS X-2 system has individual plugs for each slot, you will usually see an fcs sticker on the deck of the surfboard directly over the plugs, the stickers cover the round marks where the plug is bonded to the deck, the rings on the deck are completely normal for this type of plug but most people choose to leave the stickers in place to cover them.

FCS' Fusion plugs have one piece of moulded plastic which contains both slots for the fin, they do not have the same marks and stickers on the deck as they don't go all the way through to the top layer of fibreglass, they have the same screw pattern as the X-2 plugs.

If your surfboard is a sandwich epoxy construction you may just see the slots and holes for screws as the outer layer is opaque and covers the rest of the fin plug.

Soft boards like the Catch Surf Super One have FCS' soft board plug system, this is a piece of moulded plastic which has the two slots on one side and two threaded cylinders on the other, the cylinders go into the board and a screw goes into the deck and secures the plug through the core of the board.

Some retro fish surfboards are fitted with three FCS tabs for each fin, these are usually designed to be ridden as a twin fin with one large fin on each rail, these big fins need more support than a standard side fin so they have three tabs rather than two.

Futures Fins Plugs

Futures fins have one longer slot for each fin (around 4 1/2"s or 11.5 cm long), with a single screw hole at the front of the box, the fins are inserted into the rear of the fin plug first, hinged down into the box then the screw is inserted to secure them in place.

Futures Fin plugs in an Epoxy board and detail showing the F and X

There are two depths of Futures fin plug, the deeper 3/4" plug is used for the side fins at the front of the board and has an F cut into the box at the bottom end, the shallower 1/2" plugs are for the centre fin or the rear fins in a four fin quad set-up and have an X cut into them, the shallower box is used because the tail of the surfboard is usually too thin to support the full depth of the deeper plugs.

If you have the 3/4" Futures fin plugs at the rear of your futures quad set up and your quad fins have 1/2" tabs, you can use shims inside the boxes to make sure they are a good fit for the deeper box.

Lokbox Fin Plug

The standard and mini Lokbox fin plugs

The Lokbox fin plug also has a single slot but it's shorter than the futures one, there are two types of lokbox plug, standard and mini, both feature an oval shaped surrounding lip which you can usually see under the glass of the bottom of the surfboard.

The standard box has a slot just over 3"s long and the mini box has a slot just under 3"s long, both have a screw and plate attached to one side of the inside of the slot, this is used to secure the fin in place by placing the plate into the slot on the fin and tightening the screw.

A Lokbox fin has a single tab which is 2 1/2"s long at it's base, this allows you to move the fin back or forward inside the box and tune the performance, we'd suggest trying all Lokbox fins in the central position first.

Longboard Fin Boxes

The length of the fin box varies a little but 10"s is the norm, there will be one slot in the centre of the board at the tail, it's possible you will have one long slot for a longboard style fin and then fin plugs for smaller fins at the side, these are usually FCS, Futures or Lokbox.

This is a standard longboard fin box with fin in place, the fin can be adjusted forward or back within the box

There is a standard longboard fin box width which should allow nearly all longboard fins to fit, the nature of installing a large fin box means there is a chance your fin box might be fractionally different to another surfboards and some fins may need a shim (supplied with most FCS and fluid foils longboard fins if they're loose, or some light sanding if they're too tight to fit in your surfboards fin box.

FCS have updated their longboard fins to their FCSII system adapting the fin to simply clip in to existing longboard boxes. You can see this explained below:

Other fin set-ups

NSP and Surf Series surfboards have a separate style of fin box, the fins are connected using a bolt through the top of the board, there are several similar systems to this which may or may not be compatible, you often see them on kite surf boards and windsurf boards.

Softboard fins don't exactly have a fin plug, the fins are secured through the board by using a plastic screw, you can usually see the circular tops of the screws on the top of the board near the tail, you can loosen or tighten them using a coin.

Permanently attaching fins to the board still remains a popular choice for some professional surfers and many retro board enthusiasts, if the fins on your new surfboard are fibre glassed to the bottom you will not be able to change them and if you snap or damage one we'd recommend taking the surfboard to your nearest repair centre or shaper to get it fixed.


If you've already got some FCS fins, or just want to expand your choices of fin you might well be able to get an adapter to fit into your fin plugs which allows you to use FCS fins in the plugs you have.

Lokbox make the Grip-its which fit into the standard and mini sized Lokbox plug and can be used with any of the standard two tab FCS fins.

NSP have the NSP-FCS adapter which screws into their boards, the FCS fins go in first and are secured by two screws, one at either end, before the adapter is bolted through the deck as usual.

FCS themselves make the longboard box adapter for any standard longboard fin box, so you can use a standard thruster set in your longboard with side bites.

Surfboard Fin Accessories

Most sets of FCS and Futures fins are supplied with a fin key but you can buy them if you've lost one or just want a spare, Futures fin keys and FCS Fin keys are interchangeable - you can use either fin key with either type of fin plug, however the grub screws for each type use different thread sizes, if your board has come without the necessary hardware you can buy packs of replacement screws for Futures, FCS, Lokbox and your longboard fin box.

Many types of Longboard fin bolts are available, from standard screws which you can use a screwdriver to tighten, bolts which can be tightened by hand and the smart-screw which has the same hex pattern bolt as Futures and FCS screws so you can use one fin key for all your fins.

You might find yourself with a surfboard which does not seem to use any of these fin systems, most modern surfboards feature one of these types or at least a different brand which is compatible with one or more of the fins mentioned above.

If you don't know for sure which fin system you have give us a call on 01548 800567 or an e-mail at and we'll be happy to help.