Pentair BFS and BBFS Basic Filtration Systems consist of either two or three filter housings, which are mounted in series, a wall-mounting bracket and hardware.The BFS-201 features two 3/8" NPT low-profile Slim Line Housings in series for installations where space is limited. The BBFS systems consist of a series of large-capacity 1" NPT #20 Big Blue housings allowing for greater cartridge capacities and higher flow rates. All systems are equipped with a pressure relief button to relieve housing pressure during cartridge changes, and are shipped completely pre-assembled, saving valuable installation time.