You might notice that your FCS surf fins don't fit exactly flush on your board. There might be a gap in the front or back of the fin that can create drag and collect debris. Most people think that you just file down the fin tabs to make them fit deeper in the FCS plugs..That won't work. This is because the bottom of these fins are actually flat. You have to customize the angle and depth of the fin to fit properly. This video will show you how to fit FCS surf fins flush on your board.