These are a Flourscent Chartreuse or Hot Pink high visibility braided nylon line. They come mounted on a plastic tube shape holder. Slide your line through the nail knot tube holder slide the nail knot off the tube onto your line, leave the ends long enough to tighten on your line and remove the plastic tube holder. Then snug up the Nail Knot, by pulling both ends of the braided nylon line, slide into position, and tighten down. Don't cut the nylon line ends to short, you'll need them to tighten Nail Knot while fishing.