FCS stands for Fin Control System. Originally designed in the early 1990s, FCS is the most successful, widely used surfboard fin system in the world. The fins have two tabs or plugs that are secured to the board using set screws. FCS recently launched the FCS II keyless Fin Standard, meaning fins can be installed or removed without a key or grub screws. FCS II is also backwards compatible, meaning you can use your old dual tab FCS fins with the new FCS II system. A compatibility kit is required.