Koso North America Aluminum Washer for O2 Sensor Plug XT001BG812 Available as a set or individually Weld-in O2 sensor bung allows installation of O2 sensors in any exhaust system; 18mm x 1.5p O2 sensor bung plug works with any O2 sensor bung; 18mm x 1.5p Aluminum bung plug washer fits any 18mm O2sensor bung plug