With the Bulletproof Design of the Hollis HP5 Non-Balanced Flow-By Piston First Stage the H-O2 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 Identification. The Hollis H-O2’s First Stage Regulator comes with a 300 BAR/4500 PSI DIN Connection. The DIN Hand-Wheel Connector comes in Oxygen Green for Easy Identification for Oxygen-Use-Only. The H-O2 is manufactured from Durable and Corrosion Resistant Marine-Grade Chrome Plated Brass, has 4 LP 3/8″ Threaded Ports and 1 HP 7/16″ Threaded Port.