The FCS II Pivot Performance Glass 10" Longboard Fin is a loose fin for performing tighter turns Pivot in the pocket, lock the rail on the wave face and run the nose. Upright fin with minimal sweep and base. Loose fin for performing tighter turns. Bigger sizes ideal for logs and nose riding (9" 10"). 2 1 Compatible. Designed to be used in most existing FCS Longboard boxes. No new box required.