A tee is used to either combine or split a fluid flow. Most common are tees with the same inlet and outlet sizes, but 'reducing' tees are available as well. Tee-fittings are also an integral part of the computer-enthusiast level watercooling solutions found in many modern enthusiast PCs. The fitting is one of the three main components of a T-Line, alongside an end-cap or fillport and a length of tubing. They are plumbed into the system, with the perpendicular barb (and its attached stretch of tubing leading to a fillport or a cap).