TW30-1812 Stainless Steel RO Membrane Housing - High detail and quality. This high end Stainless Steel RO Membrane Housing fits standard residential TW30-1812 RO membranes, which is the most common size of reverse osmosis membrane for home RO systems. This SS Membrane Housing is the finest quality housing we have ever seen for residential RO systems. It is the last membrane housing you will ever need to buy. In stock for same day shipping. Learn More