5 piece brass o-ring gasket, compatible with CGA870 yoke type regulator only. Its function is to prevent oxygen leaks between the tank and the regulator. It is generally used for portable cylinders (M2, M4, M6, M9, D, E) which, due to their size, must be refilled more frequently than large cylinders. This packaging is reusable between refills, unlike those that are made of plastic. ATTENTION HOURS Monday to Friday from 9:00 am to 6:00 pm. SHIPPING POLICIES If you purchase the product before 1:00 pm, it will be shipped the same day. Otherwise the shipment would be made the next day (as long as it is working).