This is the Aqua Lung Helix Regulator 1st and 2nd Stages Features: Balanced Diaphragm A balanced diaphragm provides superior, consistent performance Yoke or DIN Available in yoke (3,300psi/232 bar max.) or DIN (4,350psi/300 bar max.) HP/MP Ports and "T" Shape 2 HP ports (7/16") and 4 MP ports (3/8"), perfectly oriented in a "T" shape for streamlined hose positioning, reduced exhalation effort, and sending bubbles out of your field of view up to EAN 40 Compatible with up to EAN 40 right out of the box Second Stage Pneumatically Balanced Pneumatically balanced for smooth, easy breathing Comfo-Bite Comfo-Bite mouthpiece is soft yet sturdy and reduces jaw fatigue with its unique palate bridge Venturi Knob Easy control: the in-line ergonomic Venturi knob lets you make precise adjustments, even while wearing gloves Specs First Stage Models: Yoke, DIN, Supreme Yoke, Supreme DIN Type of first stage: Balanced diaphragm design Auto-Closure Device (ACD):No Number of HP ports: 2 Number of MP ports: 4 1st Stage Flow Rate: 1450 l/min 1st Stage Weight in DIN: 510 g 1st Stage Weight in Yoke: 700 g Environmental Dry Kit: no First stage exterior: Chrome over marine brass Second Stage Type of second stage: neumatically balanced Controls: Venturi switch Breathing resistance: Preset Mouthpieces: Comfo-Bite Lip shield: no 2nd Stage Weight: 175 g Hose length: 730 mm Overall work of breathing (WOB) scores: Avg. 0.80 joules/liter Nitrox compatible:Yes, to 40% O2 when new, out of the box When comparing performance with price, Helix is a must have. This mid-range regulator has balanced first and second stages. It represents the DNA of the Aqualung regulators.