FCS II Infill Kit Durable silicone construction: The infills are made from high-quality silicone rubber, designed to withstand extreme temperatures and corrosive conditions without damaging plugs or fins. Compatibility enhancement: These infills replicate the flush leading edge of newer fins, improving the performance of older, dual-tab FCS fins within the FCS II system. Complete kit contents: The kit includes one center compatibility infill, four side compatibility infills, ten grub screws, and one FCS key for installation. FCS II Compatibility Infills are designed to fill the gap, literally, between the front tab of the original (dual tab) FCS fin and the front of the FCSII plug front slot. These infills are made from high quality silicone rubber which will not damage the plugs or fins (they are also extremely durable, light and built to withstand extreme temperature and corrosive conditions). Includes Centre Compatibly Infill (x1) Side Compatibility Infills (x4) Grub Screws (x10) FCS Key (x1) Reusable zip lock bag FAQ Will my old FCS (dual tab) fins work with the FCS II system? Yes, you can use all your existing FCS fins with the FCSII system; however the FCS MF-1 fin pictured is not included. The FCSII plugs are backwards compatible - grub screws can be used within the FCSII plugs to secure your existing dual tab FCS fins. FCS has designed a set of unobtrusive silicone infills to fill the gap created by the old fins in the new system. The infills are made from high quality silicone rubber which will not damage the plugs or fins. They are also extremely durable, light and built to withstand extreme temperature and corrosive conditions. The infills replicate the flush leading edge of the new fin design improving the performance of the old fins. Fin System: FCS II Fin Type: Infill Kit Type Highlights: 1 Center Plug Infill and 4 Side Plug Infills