Oxygen Sensor Port Plug
Racing Beat LLC
Product information "Oxygen Sensor Port Plug"
This plug can be used to seal the oxygen sensor port when the sensor is not being used. As compared with the common technique of "welding" the port closed, the use of this plug provides a convenient method to retain the usage of the sensor port for later use.
The specifications for the fitting are: 18mm x 1.5 Pitch - SUS 304.