Greenough 4A
The Greenough 4-A Single Fin is the most iconic, functional and versatile single fin available, because it works extremely well on just about every type of surfboard.
The Fin
The Greenough 4-A Single Fin is the most iconic, functional and versatile single fin available, because it works extremely well on just about every type of surfboard. The 4-A has been True Ames' bread and butter for over 40 years now, and it is still the most popular single fin design there is due to it's all-around and well-balanced performance.
Form | Medium profile, full base coupled with a tapering & moderately flexible tip
Function | A fin that will hold when you need it to and release when the time is right
Feel | Neutral-positive, perfectly-balanced, a fin that will drive off the bottom, and have an acute responsiveness through arcing turns
Overall | Versatile - designed for all board shapes and surf conditions
Specifications
The Designer
George Greenough
Santa Barbara, California
Widely considered the father of the modern high-performance fin. His designs revolutionized how surfers think about flex, rake, and hydrodynamic flow. The Greenough 4A is the culmination of decades of refinement — a fin that balances drive, hold, and release in a way that feels intuitive in every condition.
Size-by-Size Measurements
Height, base, area, and weight for every 4A size. Specs confirmed across True Ames and Cleanline Surf.
| Size | Height | Base | Area | Weight |
|---|---|---|---|---|
| 6.5" | 6.49" | 5.42" | 22.86 sq in | 227g |
| 7.0" | 7.09" | 5.67" | 24.89 sq in | ~255g |
| 7.5" | 7.55" | 5.95" | 26.86 sq in | ~280g |
| 8.0" | 8.11" | 6.09" | 28.85 sq in | ~305g |
| 8.5" | 8.51" | 6.42" | 32.19 sq in | ~330g |
| 9.0" | 9.14" | 6.93" | 36.13 sq in | ~355g |
| 9.75" | 9.71" | 7.09" | 39.93 sq in | ~380g |
| 10.0" | 10.08" | 7.42" | 43.85 sq in | ~400g |
| 10.5" | 10.63" | 7.91" | 48.44 sq in | 425g |
Technical Details
Specs no other retailer publishes.
Moderate-to-heavy. More swept than a pivot fin (~28°), less than a hatchet (~40°).
Industry standard for all single fins — equal shape on both sides for balanced rail-to-rail performance.
Screw + plate. Does NOT fit Futures or FCS boxes. For 2+1 setups, buy the 2+1 Combo pack.
Matte finish. Volan version uses hand-laid volan cloth with raw finish — flex from the body, not just the tip.
Inspired by bluefin tuna caudal fins. High-aspect-ratio design that launched the shortboard revolution.
Sizing Guide
Start with 1 inch of fin per foot of board, rounded up to the nearest available size. You can go up to 1" larger for heavier riders, narrower tails, or overhead waves. For 2+1 setups, drop 1.5–2" from your single-fin size — the side bites add hold, so the center fin can be smaller.
| Board Length | Single Fin | 2+1 Center |
|---|---|---|
| 5'6" – 6'0" | 6.5" | — |
| 6'0" – 6'6" | 6.5" – 7" | 6.5" |
| 6'6" – 7'0" | 7" – 7.5" | 6.5" – 7" |
| 7'0" – 7'6" | 7.5" – 8" | 7" – 7.5" |
| 7'6" – 8'0" | 8" – 8.5" | 7" – 7.5" |
| 8'0" – 8'6" | 8.5" – 9" | 7.5" – 8" |
| 8'6" – 9'0" | 9" – 9.75" | 7.5" – 8" |
| 9'0" – 9'6" | 9.75" – 10" | 8" – 8.5" |
| 9'6" – 10'0" | 10" – 10.5" | 8.5" – 9" |
| 10'0"+ | 10.5" | 9" |
Size up if you're over 200 lbs, riding a narrow-tailed board, or surfing overhead+ waves. Size down for wide tails, small gutless surf, or if you want a looser feel. For 2+1 setups: the larger your side bites, the smaller the center fin can be.
Why Volan?
Volan is a woven fiberglass cloth laid by hand and finished with a resin that cures to a warm amber tint. It flexes differently than solid fiberglass — more spring, more life, more feel through turns. Where solid glass is stiff and direct, volan breathes with the wave.
The hand-laid process means each fin has subtle texture and character. It's heavier, which adds momentum through flat sections. Surfers who ride volan describe it as "warmer" — the fin does more of the work, trimming and holding without demanding constant input.
Shop the Greenough 4A Volan ›
Greenough 4A
The Greenough 4-A Single Fin is the most iconic, functional and versatile single fin available, because it works extremely well on just about every type of surfboard.