Performance Fins have a rigid core that creates good drive and projection off bottom turns and cutbacks. The combination of the flexible edges and rigid core will help to make your board ride smoother, faster, and easier to turn. This will allow you to surf better, reduce fin injuries, and add more fun to the sport of surfing! Pro Teck Performance Fins with the rigid core are recommended for intermediate to professional surfers.Shortboards4" for surfers under 100 lbs.4.25" for surfers under 150 lbs.4.50" for surfer over 150 lbs.Longboards7" Center Fin9" Center Fin4" Side FinsPro Teck Fins are surfboard fins with flexible leading and trailing edges designed to enhance board performance and reduce fin cuts. The flexible trailing edge allows the water to flow smoother with less turbulence off the fin. The flexible edge also creates a "rudder action" as the water pressure bends the edge, creating tighter and more fluid turns, similar to the fins of dolphins and sharks. The flexible urethane edge also greatly reduces fin cuts compared to conventional hard edge fins. Center Fin Design The center fins have a streamlined leading and trailing edge that is soft and flexible, making the fin flow smoothly through the water.Side Fin Design The side fins are designed with a "rounded" or "radiused" leading edge that makes turns smoother and forgiving. The trailing edge is designed with an exclusive "beveled" inside edge that allows the water to release off the fin faster and smoother than conventional fins that have a flat or dull trailing edge. Pro Teck Fins are the only fins that have streamlined or "sharp" trailing edges that are soft and flexible, that will greatly reduce fin cuts!