Normally these units are used in a vertical position (height 40″) but where clearance is limited, horizontal adapter kits are available (from 7″-14″). Each is equipped with standard shallow pleated 40 micron, reusable polyester cartridge filters, and a pressure gauge and air relief valve. All PVC construction, no metal parts. Operating pressure 0-80 PSI but can withstand hydrostatic pressures of over 450 PSI. Hand tightened, “O” ring sealed, screw caps for easy access and large screw plugs for quick draining. Can be plumbed so that water comes in and out on same side or in one side and out the other. Multi-cylinder units fill up in parallel, not in series. Support base is elevated and has holes for secure mounting. Several optional cartridge styles available including shallow pleated cartridges capable of filtering to 100 microns and inner chamber chemical cartridges, for holding carbon, zeolite, resin or other granular products. GPM are recommended gallon per minute. Max = maximum flow rate. Inlet/outlet fittings on M1, M2 are 1.25″ FPT (female threaded) all other units are 1.5″ FPT.