Used to prevent over pressurization of the Low Pressure side of a 1st stage that does not have an integrated safety relief and uses G 1/8 threading for ports. For diving regulators this would be placed in the 1st stage when upstream Second Stage regulators are used (e.g. Xstream and Jetstream). This is also used to protect the Intermediate Pressure gauge in the Poseidon 3460 Test Box.