Pro Teck Power Flex Smoke 3 Fin Combo Set Includes 9" Center Fin / 4" Side Fins Pro Teck Power Flex Combo FCS 9.0+4.0 Smoke. Power Flex is a Pro Teck Fin with a medium core flex. The fin bends on turns, and then springs back, creating forward thrust similar to a swim fin. The medium flex core and flexible trailing edge makes the board turn smooth and fluid, with continuous speed.