To fill the gap between the front tab of the original (dual tab) FCS fin and the front of the FCS II plug front slot.No you can’t put your fins in backwards….but you can use all your favorite original FCS fins in the new FCS 2 boxes by using the FCS 2 adapter kit complete with flush forward fairing kit.Check out the pic of Trips Stretch PCs in the new FCS 2 boxes on a …Lost MC Metro.