Stainless steel connection built for Reverse Osmosis water storage tank; pump tank & thermal tank applications. Brass cap with internal O-ring guarantees no air loss from air-vent. Smooth internal air vent cap prevents diaphragm damages. High-grade butyl diaphragm, post-cure procedure insures a tasteless and odorless water chamber NSF 61 and 58 listed, IAMPO approved, and CE Mark approved.