Panel-mounted RCA pin jacks and φ3.5 jacks are classified into "insulated" and "non-insulated" types. Insulated or non-insulated refers to whether the GND terminal of the connector touches the panel when the connector is attached to the panel.
In the case of the insulation type, the GND terminal of the connector is not connected (contacted) with the panel.
The non-insulated type is electrically connected when the panel is metallic. Insulated connectors are used when you do not want to create a "ground loop." *A GND loop is a loop of wire, and a loop of GND wire in particular is called a "GND loop." When the magnetic flux chains with the loop, a current flows through the GND line, which generates a voltage and causes noise. In such a case, cutting the loop can prevent the noise caused by flux cross-linking.