Series 40™ Heavy-Duty single-stage regulator regulators are extremely durable and contain our exclusive Sure Seat™ filtered seat technology for extended seat and regulator life in the most demanding industrial applications. They feature a stainless steel diaphragm which allows for use with liquid gases, all brass construction which will stand up to corrosive atmospheres and 2.5-inch (64 mm) brass case gauges. Included HB190 Hard Hat™ gauge/regulator guard.