Standard Size Reverse Osmosis Membrane Housing with built-in 0.3cm quick-connect fittings.Standard Residential Membranes made By Filmtec, GE and many others, ranging from 18 to 378.5ls Per Day, will fit in this housing.If you are replacing a membrane housing that has threaded fittings, you may need to replace your cheque valve.Many housings with threaded fittings have the cheque valve built-in to the threaded fitting in the centre port on the end with two ports.Our CV-10 push-in cheque valve(Please look at our store list) is ideal for use with HM-QC.A cheque valve is required for proper functioning of an under sink reverse osmosis system that uses a bladder tank.(CV-10 add $4.2 if you need and no addition shipping charge)