These Stainless Steel Membrane Housing O Rings come in a set of 4. There are two 4" and two 1" included in this set. They're designed for stainless steel membrane housing caps, for the outer and interior caps. Each cap typically takes four O Rings, if you're looking to replace each side of your membrane housing, you'll need two sets.
This set fits standard 4" X 40" stainless steel commercial membrane housings. Any questions about sizing or set details, our expert customer service department can help, call 1-888-309-2837.