Big Blue units use standard-sized high flow vessels that are capable of delivering 16 gallons per minute. They also use larger 4.5" X20" filter cartridges for increased filtration capacity. Big Boy units come with 1.5" FNPT (female nipple pipe thread) Ports for minimized pressure drops and comes with a UV lamp only. These are tough, heavy-duty units built to deliver very clean, bacteria-free water. Specifications: Maximum Flow: 16 gallons/min Replacement Lamp Size #: 20