This is the Apeks ATX40 Scuba Diving Regulator

Features:

• Highly Technical Design
• Braided 3/8 Flexi-Hose
• Total Weight: 39.86 oz. (1130 g)
• Nitrox Ready Up to 40% O2 Out-of-the-Box
• Suitable for Cold Water Use Below 50°F (10°C)
• First Stage: APEXS ATX40 DS4:
• Unique Over-Balanced Diaphragm First Stage
• Chromed Marine Grade Brass Construction
• Environmentally Sealed to Keep-Out Contaminates
• Delicate Internal Parts Not Exposed to Contaminants: Salt, Sand, Chlorine or Pool Acids
• Requires Less-Maintenance
• Secondary Environmental Diaphragm Membrane:
• First Stage Completely-Sealed-Off
• Dry Ambient Pressure Chamber
• Second-Layer of Corrosion Resistance and Prevention of Freezing in Cold-Water-Use
• Four 3/8" UNF (Unified National Fine) Medium Pressure Ports
• One 7/16" UNF High Pressure Port
• HP & MP Ports Angled for Optimum Hose Routing
• Second Stage: APEXS ATX40
• Pneumatically-Balanced Second Stage
• Smooth, Easy Breathing

The APEXS ATX40 uses the DS4 first stage. Unique over-balanced, diaphragm design - as the diver descends, the over-balancing feature allows the medium pressure gas in the hose to increase at a rate faster than ambient. This results in superior performance at depth. An environmental dry system keeps water out of the main spring chamber thus preventing ice build-up and keeping silt and contamination out. The chromed marine brass first stage has four medium-pressure (3/8" UNF) ports and one high-pressure port (7/16" UNF). "