I need to know the diameter of the stock O2 sensor bung on the midpipe.

I want to place another bung on the MP for dyno wideband tuning.

 

First of all, the stock 02 sensor bung is on the pre-cat or downpipe, not midpipe. Secondly, why do you want the size of the stock bung? What you need to know is the bung size required by the wideband 02 sensor you will be using. I would assume you were buying some type of kit or pre-manufactured wideband, both of which will come with a bung for the wideband 02 sensor.

 

Yes, on the downpipe.
To plug the wideband sensor at the dyno.

Do you know the diameter?

 

18 mm If you need the pitch I will call Garfinkle and ask.

 

I just took my pipe to a muffler shop and told them I needed a new o2 bung welded on...
I guess I got lucky, I didn't realize O2 sensors had different threads...I guess it makes sence. Why make everything fit together!?

 

i think it's 18mm x 1.5 pitch

 

I just had one welded on; it is 18 X 1.5. I paid $10 for it from a local speed shop.