I may be purchasing aftermarket headers for one of my projects. Most of the options I care to look at do not have O2 sensor bungs welded in them, so I'd have to purchase some and weld them in so the computer can work correctly. The bungs I see advertised for O2 sensors are M18x1.5 ... Is this the common size for O2 sensors? Are there other sizes? If so, what do those apply to?

2 Answers 2


There is no overall standard here although M18x1.5 appears to be relatively common. I recommend that you pick the O2 sensor you intend to use for this application and then weld on the bung for that particular model. Otherwise you run the risk of having to redo your welding.

  • What other sizes do you see? Mine definitely isn't M18x1.5. Mine seems to about 1/2" diameter.
    – KyferEz
    Commented Jan 6 at 21:53

Of course you could weld a blank bung and then drill & tap to the correct size.

  • This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review
    – Chenmunka
    Commented Apr 16, 2020 at 17:26
  • @Chenmunka drilling and tapping a new bung to the correct thread is a valid method of being able to fit an oxygen sensor4 whether you think so or not.
    – Solar Mike
    Commented Apr 16, 2020 at 20:04

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