Could you help me with the size of this nut/bolt. Exhaust.
 

I tried to remove the pre-cat O2 sensor on the driver side and the threading on the sensor was left in the bong. That sensor is in a tight spot. I did heat it but I guess it wasnt hot enough. Now I have to drop the exhaust then re-thread the bong. I was looking at the nut which attaches the exhaust to the manifold and I am not sure if its a nut or what. It looks weird. But on RealOem, its a normal nut for that location.

Any help will do.
Thanks