The TRIO is a horizontal mounted polymer peep sight mounted by splitting the string into three strands a 120-degrees. Preferred by archers who want the security of knowing no more than one strand will ever cross the aperture hole assuring that vision will never be completely obstructed. Each packaged blistercard includes two peeps 4mm/5mm & 5mm/6mm. You should never use a horizontal polymer peep in bows exceeding 330fps IBO.