ITEM NAME:Professional Future Base Fins Quad Fins Surfboard 4 fin Set Fiberglass Description: Those quad fins apply to most surfboard/shortboard/funboard/ longboard that use futures fins base system Made of qualified 70% nylon and 30% fiberglass with great durability, lightness and flexibility 2 pieces F4.37'' (left, right) works for 3/4 fin box and another X3.5'' (left, right) works for1/2 fin BOX Quad Fins helps to hold and change direction to increasing surfing speed Great for big wave surfers and different surfing style Specification: Plug thickness: 7.1mm  ± 0.1mm Color: Black Package Includes: 4 Pieces Surfboard Fins Note: Please allow slightly difference due to manual. Thanks SKU: DMO0013515754041940.4 Pieces Surfboard Fins. Those quad fins apply to most surfboard/shortboard/funboard/ longboard that use futures fins base system. 2 pieces F4.37" (left, right) works for 3/4 fin box and another X3.5" (left, right) works for1/2 fin BOX.