Pin-Index Safety System (PISS), a system for identifying connectors for certain small cylinders of medical gases that have flush valve outlets rather than threaded outlets. The identifying code consists of a specific combination of two holes in the face of the valve into which connecting pins for a particular type of gas must fit in perfect alignment. For example, the index hole position for a cylinder of oxygen is 2–5, for nitrous oxide it is 3–5, and so on. See also Diameter-Index Safety System.
