CGA, the Compressed Gas Association, establishes the safety standards for the industrial gases industry.
To help keep people safe, CGA has developed a system for categorizing connections to deter misuse and incompatible configurations. So, what does a CGA 3-digit number mean? CGA valve outlet connections are identified by a 3-digit number relating to the rated or maximum cylinder pressure at which the connection is designated to be used, the gas type, and a designation of the valve outlet thread when applicable.
Each connection has its own dimensions including manufacturing tolerances. This serves to ensure the interchangeability of parts from different manufacturers, as well as preventing interchangeability with other cylinder valve connections that would result in a hazardous cross-connection.