FCS K2.1PC Tri Fin Set. Kelly Slater’s signature fin for hollow waves and tight pocket surfing. Performance Core (PC) material and construction is designed to deliver the feeling of a traditional glass fin with the added performance of reduced weight. The result is a lightweight fin with remarkable flex, a smooth feel and an impressive aesthetic. Base: 4.33" 110.0mm; Depth: 4.53" 115.0mm; Area: 15.23" 9824mm; Sweep: 32.0; Center Base: 4.28" 109.0mm; Depth: 4.41" 112.0mm; Area: 14.22" 9172mm; Sweep: 31.0. FCS.