Pin Index Safety System

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Pin index dimensions.JPG
Pin numbers.JPG

The Pin Index Safety System, or PISS, is a safety system that uses geometric features on the yoke to ensure that pneumatic connections between a gas cylinder and a machine that uses pressurized gases are not connected to the wrong gas yoke. This system can be seen on an anesthesia machine.

Each gas cylinder has a pin configuration to fit its respective gas yoke. Refer to the figure on the right; units are in millimeters.

  • O2: 2-5
  • N2O: 3-5
  • Air: 1-5
  • CO2: 1-6
  • He: No pin
  • Cyclopropane:3,6
  • Mixture of O2 / He (He ≤ 80%, commonly called Heliox): 2-4
  • Mixture of O2 / N2O (50% / 50%): 7 (a single pin, located in the centre)
Pin index yoke connector for medical oxygen filling whip
Detail of pin index yoke connector for medical oxygen
Pin index medical oxygen cylinder valve


  • International (ISO) and European (CEN) Standard
  • EN ISO 407 : Small medical gas cylinders - Pin-index yoke-type valve connections

The pin index system is a safety system (PISS) designed to ensure the correct gas is filled into the correct cylinder, and that the cylinder will only connect to the correct equipment. The positions of the holes on the cylinder valve correspond with the pins fitted to the yoke attached to the equipment. The pin positions for each medical gas are unique. If an attempt is made to fit the wrong gas cylinder to the yoke a tight seal will not be made, as the pins cannot locate.