It's a safety valve (no pun intended). Specific valve outlet connections have been designed for most gases to prevent their misuse or contamination. In fact, Standard V-1 published by the Compressed Gas Association has detailed dimension drawings of 115 valve outlet connections for nearly 268 different products. The scope of this standard is to provide connections that minimize the possibility of hazardous misconnections between non-compatible gases. This is accomplished by providing detailed drawings and gas assignments for outlet connections and the test protocol by which these and future connections are approved.