Watts Premier OEM 50 GPD TFC RO Membrane W-1812-50 Watts Flowmatic W-1812-50 RO Membrane is a 50 gallon per day reverse osmosis thin film composite (TFC) membrane. Fits most standard RO units including but not limited to the Flowmatic FMRO4J, FMRO4G, FMRO5G, FMRO5GP, and model 5SV. The W181250 membrane is 1.8" x 11.8" Membrane should be changed every 2-5 years depending on water quality and usage. **Please note the design of this filter has been improved to enhance its performance. The black band which was located at the end with the 2 o-rings is now on the opposite end. This membrane will still fit all systems as well, if not better, than it did before the design change