FCS Fins - FCS II Harley Ingleby Performance Gl... Centre fin can be inserted, removed or adjusted in seconds. No screw and plate required. Centre fin fits a variety of existing single fin boxes. Please Note: the side fins are designed to be used exclusively with the FCS II Fin System, and will not fit in the traditional FCS Dual Plug System. Ideal for performance longboards, surf SUP's and 2+1 set-ups