This is an angled O2 bung that helps for clearance in your downpipe tunnel. Sometime with larger downpipes the O2 sensor can run into the side of the exhaust tunnel, this bung can help move it away from clearance issues. There are two versions: there is a thread in one that can thread into your factory o2 bung and be turned 180 degrees to clear the car, or there is a weld in version.

Not for use on primary O2 sensor.