The 7" Single Fin by FCS II is a full bodied template providing a stable and predictable feel. FCS II Single Fins utilise a patent pending technology that eliminates having to screw in your fin. Compatible with your average single fin box. Available in sizes 6" - 8". As a guide if you are looking for a single fin for an 8ft board get the 8". If you are using trailer fins you can easily drop down sizes.