An attempt by Union Connector in the late 1970s to build a locking stage pin connector. The center ground pin had a retractable "hook" that would lock into a socket on the female. In practice, this hook was easily broken and the line was discontinued.
See also http://www.controlbooth.com/wiki/Collaborative+Articles:Connectors+Stage+Pin .
See also http://www.controlbooth.com/wiki/Collaborative+Articles:Connectors+Stage+Pin .
