Dorsal Performance Flexrez Core Surfboard Thruster Surf Fins (3) FCS Compatible Red This Red FCS Compatible FlexRez Thruster Surf Fin Set allows for a moderate amount of flex that while having a lighter material the flex pattern still allows you to have smooth transitions through turns the inside foil technology provides freedom in performance. Another favorite of the pros and beginners alike this fin will suit the any surfer or those who want to push themselves to the limit. For surfers in the 100 to 180 pound range. Base: 4 5/16" Depth: 4 1/2" Area: 14.3 sq. in.