Flex Fins. My Flex Fin designs are the outcome of decades of thoughtful refinement. My “A” Series Flex Fin template has a lower aspect ratio (wider base, more “rake” and area) as compared to the “B” Series Flex Fin template which has a higher aspect ratio (narrower base, less rake, less area). Typically the “A” Series templates provide stability and run-out for surfboards that work more off of the tail such as single fin mini-guns, single fin mid-range-guns, big wave boards, single fin long-boards and fun-shape types. My “B” Series templates have evolved as an essential component of My thinner railed “Hull” designs from the late 1960’s to the present day. Best suited at the point where the rail of the surfboard takes over on a carving type rail turn. Think point breaks with long sectioned hollow waves! The “Series Flex Fins” are foiled with a neutral mid range flex. These fins are ready to go to work immediately. As with any hi-performance design, fine tuning has always been a basic assumption. Feel free to reach out if you have questions on our Contact Page link. https://www.shapesandhulls.com/contact Ride waves, Tim Bowler