You are standing over your board looking at two holes, and you cannot tell anyone what they are called.

That is the whole problem. Not fin choice — you have probably already decided you want a twin, or a bigger trailer, or that the stock thrusters are wrong. What stops the order is hardware someone else installed years ago, that nobody labelled, and that every product page describes with the word compatible.

"Compatible" is doing quiet work there. It does not mean made by. A True Ames fin described as "FCS Compatible" is not an FCS fin — it is a True Ames fin with a base cut to go into an FCS box. Usually that costs you nothing. Twice below it costs you something real.

Name it in about a minute

Go and look at one side-fin position and count what is in it.

Two small plugs, each with a grub screw → original FCS. You tighten it with a hex key.

One long slot per fin, and nowhere to put a hex key → FCS II. FCS's own pitch is that you "install and remove your fins in seconds without the need for any screws or tools," so the tell is the absence of hardware.

One long box per fin with a single screw at the front → Futures. A full-base system: the whole base seats in the box rather than two tabs.

One long slot down the stringer with a track inside → a center box, which True Ames calls the US Universal Bahne box. Every one of our 108 single fins goes in it, which is why almost none of those pages mentions a system. There is no decision to make here.

You should be able to finish the sentence my board takes ____ now. If you cannot, photograph the fin area and send it to us. Faster than reading this twice, and free.

If it's FCS II, read this before you order

True Ames publishes exactly four base types — Bahne box, FCS, Futures, glass-on — and FCS II is not one of them. If your board is FCS II, no fin in this shop is native to it.

Not a dead end. FCS sells the FCS II Compatibility Kit at $20.00, and describes what it does precisely: the silicone infills "fill the gap between the front tab of the original (dual tab) FCS fin and the front of the FCSII plug front slot," and "will not damage the plugs or fins."

The direction matters. Old dual-tab fin into an FCS II box: yes, with infills and screws. That is the direction you need. The other direction — an FCS II fin into a two-plug box — has no part; FCS makes nothing that does it.

The kit costs more than $20.00, though. You give up the keyless part: a dual-tab fin in an FCS II box is a hex-key job every time, which is the convenience you paid for with the board.

The two things that actually bite

Futures boxes are not all the same depth. They come in 1/2" and 3/4", with assigned jobs. The 3/4" is "for the front side fins of a thruster, quad, 5-fin or 2+1 set-up"; the 1/2" is "for the center trailing fin and quad rear fins."

So a quad has both — fronts deep, rears shallow. Buy a fin with a 3/4" base for a rear quad position and it does not go in. True Ames prints the warning on the 2.6" Side Bites Futures page itself: "This 3/4" Futures Fin Base Does Not Fit For Rear Quad." That is a property of the boxes your shaper installed, not of the fin. A different template does not change it.

Three templates are not identical across the two systems. Twenty-six publish the same height, base and area either way, and 59 of the 60 template-and-construction pairs offered in both are priced the same — so take the system dropdown as a real choice, not a colour swatch, but do not lose sleep over most of the range.

The one that is worth knowing about is the Mackie Sidecut Fish Keel: the Futures version is published with 0.20" less base and about 4% less area per fin than the FCS one, and True Ames prints both inches and millimetres for it, agreeing in both listings. Order the Futures one expecting the FCS fin and it is a slightly smaller keel.

The Mandala DELTA-V pair differ by an amount we read as rounding. The Timmy Patterson Tri is the strange one — identical published height, identical published base, areas about 5% apart. Two figures say one thing and a third says another, nothing published resolves it, and we will not guess. Ask and we will measure a pair.

Glass-on, and what removability costs

Glass-on fins have no base to fit anything. They are laminated on by the glasser, permanently, and the decision gets made once, usually by someone else, before you own the board.

The price gap is the interesting part. True Ames offers eight templates both ways in solid fiberglass, and glass-on runs 40% to 50% less across all eight. Same foil, same template, roughly half. The difference is the moulded base and the tooling for it.

That is what you are paying for when you buy a removable fin, and it is not a small line item.

We do not carry glass-on — zero of our 299 fins. That is a conversation with a shaper, or with us.

What to buy, by the box you just named

Futures. The best-supplied case: 123 of our 191 multi-fin products come in a Futures base.

  • Thruster → KC Tri, $128.50 fiberglass or $123.50 Hexcore. True Ames' own words: "the all-around powerhouse for the middle weights."
  • Quad → True Ames Quad, $148.50, the house template on a normal tail; or the Mackie Quad at the same price for a fish or a wide tail. Rears only → 6-4 Rear Quad, $73.75.
  • Twin → Lovelace Twin, $113.50.
  • Side bites → 3.25, $73.75 — a hint of hold and nothing more, which is what you want under a log you are not trying to stiffen. Size up to the 3.7 at the same price.
  • Trailer → 3.3" Trailer, 50/50 foil, $39.00.
  • Asymmetrical → Lovelace, regular or goofy, $133.50. Buy for your stance, not your preference.

Original FCS. Fewer options overall — 99 products against 123 — and it inverts by category: more side-bite products here than in Futures, fewer twins.

  • Thruster → KC Tri in FCS fiberglass, $105.50. No thruster set in the shop is cheaper, in either system.
  • Quad → Album Quad, $148.50 — a conventional set with no surprises in it.
  • Twin → Stüssy Roots Twin, $113.50. Stiff and flat-foiled; built for power, not looseness.
  • Side bites → 3.25 in FCS, $73.75.

FCS II. Any row on the FCS list, plus the $20.00 kit, and accept the hex key.

A center box. Nothing above applies. Every single fin we sell fits, and the decision is depth, not system — the sizing post has it.

A center box and two side boxes. That is a 2+1, the center fin needs to come down, and that argument has its own post.

Where a row offers the same template in fiberglass or Hexcore, take the fiberglass unless you already know you want the lighter flex. The gap is a few dollars either way and it is not the deciding number.

Bring the board in, or send a photo of the tail, and we'll name the boxes for you.

Related reading

Sources