FCS2 Quad Rear Fins - Set of Left and Right Please see the photos for the size. These are rear fins that are slightly smaller than a medium-sized tri-fin. Discounts are available for those who purchase these in combination with a tri-fin set. * Size: M * Color: Black * Material: Engineering grade polymer, glass flex * Designed with a balance of speed, flow, and response in mind * Perfect for surfers looking for all-around fins * Provides a combination of speed and maneuverability.