Nanoptics Ultra Super Flex (USF) fiber is the perfect fiber for everyday use by competition pros and enthusiasts alike. As our general use fiber, it is the brightest fiber available on the market. USF fibers easily flare with heat to stay secure in your sight pin. Each replacement pack contains one 40” fiber in your choice of size and vivid color. Our fibers fit all brands of archery sights and sight pins. Check with your sight manufacturer for proper size. Nanoptics is the worldwide leader of fluorescent optical fiber. As the leading supplier, we manufacture the brightest and toughest fiber in the industry. All of our products are proudly made in the USA.