Air Fuel Ratio Sensor Thread Size

I recently swapped engines in my 2008 Prius. I am now getting an occasional P0420 error which points to the Catalytic Converter, O2 Sensor(s), etc. So, I MAY be replacing the two O2 sensors. Happens I have the Air Fuel Sensor (this is the front one that is installed in the Exhaust Manifold) because the used engine I swapped in did not have one. When I tried installing the New sensor I could not get it to thread in- acted like the threads in the manifold were munged up, or the threads on the New sensor. I was able to get the old sensor from the engine I removed to thread in so I was happy, and I now have a spare sensor.

If I have to install this New sensor, I would like to first chase the threads on the sensor and in the manifold. Does anyone know what the thread size is? I could bring the new sensor to a parts store to find a Tap and Die to fit, but if the threads on the sensor are munged up from my attempts at installing it this may be a problem...

I strongly suspect my code problem may be a dirty Catalytic Converter as the old engine was blowing a LOT of smoke when it died. I think the old engine ate the pistons, rings, valve guides, etc. from being driven 15 to 30 miles without oil. Yup no oil. Not a drop.

So I am going to run some Cataclean through it first and hope that is the fix. Replacing this front O2 sensor is NOT going to be a picnic, even with the windshield wiper cowling removed.....

Thanks in advance!
Ray L.