Dorsal FUT Fin Compatible Keel Twin Surfboard Fin Set - Bamboo The Dorsal's D1 Keel Twin Fins are a classic keel fin design. The Honeycomb material with the iconic wood inlay give the D1 a medium flex pattern and the big, old-school template generates rail-to-rail speed down the line and provides hold through direction changes. The D1 Keel is the iconic match up with your retro-fish. Features Size: Fit To Board Fins in set: 2 Material: Honeycomb Tech Specs Side Fins: Height: 5.01 in