FCS II Compatibility Infills are designed to fill the gap between the front tab of the original 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. :: Unisex > Surf Accessories. 1 X centre compatibly infill4 X side compatibility infillsReusable zip lock bagFCS Key10 X grub screws Size: one size.