Check the listing for details. Hollis HO2 Oxygen 1st Stage Regulator. Condition: New. Listed at 299.95 USD. With the Bulletproof Design of the Hollis HP5 Non-Balanced Flow-By Piston First Stage the HO2 First Stage is Certified for up to 100% Oxygen Service thanks to Highly Specialized Component Materials and Manufacturing Processes. Cleaned and Assembled in a Clean Room Environment with Specially Designed Materials, Halocarbon Based Lubricants and Color- Coded for Easy IdentificationThe Flow-By Piston Design is the only true Fail-Safe First Stage Design on the market. The Piston will automatically move Downstream from the High Pressure Air coming from the Scuba Cylinder if there is an unexpected malfunction of the High-Pressure Seat. This feature guarantees a constant Gas-Flow to the Second-Stage Regulator. The Regulator First Stage weighs 8.3 oz (235.3 g). FeaturesBulletproof Hollis HP5 First Stage DesignNon-Balanced Flow-By PistonFail-Safe First Stage Design300 BAR/4500 PSI DIN ConnectionDIN Hand-Wheel Connector: Oxygen Green for Easy Identification for Oxygen-Use-OnlyMaterial: Durable and Corrosion Resistant Marine-Grade Chrome Plated Brass4 LP 3/8" Threaded Ports1 HP 7/16" Threaded Port