02 sensor bungs are the same thread as spark plugs 14mm.
ADDED FOR MORE INFO
I wanted to add that Auto Zone etc.. sell spark plug anti-foulers. They are a kinda a spark plug extender that has a small hole in the end (maybe 3/16") near the electrode tip that keeps
oil from getting on the plug. Easy to weld up and make an 02 sensor plug = 2 bucks each. Or they sell plugs at most muffler shops for about 5 bucks each.