The Mares 28XR First Stage is a balanced diaphragm regulator in a rugged chrome body with four standard size low pressure 3/8-inch ports on a swivel turret with an additional fifth port on top of the turret. Two standard size symmetrically aligned high pressure 7/16-inch ports have a 10-degree angle for optimal HP hose routing. The first stage is environmentally sealed, comes standard with a 300-BAR DIN connector, and is Nitrox Ready.

The first stage includes their dynamic flow control (DFC) system to provide low-pressure ports with constant inter-stage pressure and gas flow unaffected by depth, tank pressure, or breathing rate. The Mares first stages also include their Auto Sealing Technology (AST) that stops moisture and contaminating agents from entering the interior of the first stage, as can happen during the surface interval when the regulator is being moved between tanks or post-dive when the regulator is rinsed.

Please note that when this 1st stage is sold "raw" as received from the factory and not part of a package, it will have four of the five LP ports plugged (i.e. one LP port will be open) and both HP ports will be plugged.