The pin index code of nitrous oxide is

The Pin Index Safety System, or PISS, is a means of connecting high-pressure cylinders containing medical gases to a regulator or other utilization equipment. It uses geometric features on the valve and yoke to prevent mistaken use of the wrong gas. This system is widely used worldwide for anesthesia machines, poable oxygen administration sets, and inflation gases used in surgery. Cylinders attach to the machine hanger-yoke assemblies that utilize a pin index safety system to prevent accidental connection of a wrong gas cylinder. The yoke assembly includes index pins, a washer, a gas filter, and a check valve that prevents retrograde gas flow. PIN INDICES OF COMMONLY USED GASES: O2: 2,5 N2O: 3,5 Mixture of O2 and N2O (50% / 50%), commonly called Entonox: 7 (a single pin, located in the center) Air: 1,5 Mixtures of CO2 and O2 with more than 7% CO2: 1,6 Mixtures of CO2 and O2 with less than 7% CO2: 2,6 He: No pin Mixtures of O2 and He with less than 80% He, commonly called Heliox: 2,4 Mixtures of O2 and He with more than 80% He: 4-6 Cyclopropane: 3,6 Ethylene: 1,3 Nitrogen: 1,4 Ref: Miller's anesthesia 8th edition Ref: Morgan & Mikhail's clinical anesthesiology 6e