Designed for triathletes or long distance training, the Zefal Tri allows you to attach two water or tool bottles to the back of your saddle. The Tri also offers two holders for small inflators and a cartridge (16 or 25 g). The bottle holders are sturdy and securely designed so that the bottles can not move. Through the side openings, the holders still provide easy access. The Zefal Tri is made of fiberglass reinforced composite and fits through the universal rail mount on any standard saddle.