Does anyone know what the tread size for the 02 after cat senor is?

 

Not aware of an O2 sensor that is downstream of the cat. They are all in front of it. I do know the O2 sensor thread is an SAE pipe thread rather than a bolt thread. Thats about as far as I can get you.

 

Yeah, your right...it is in front of the Cat, but autozone lists it as behind so I thought I'd do the same. Why the #$^*&* would you use a pipe thread?!!

 

Well because you are threading it into a PIPE of course and we are after all left to the mercy of some of the most "brilliant" people on earth... engineers! (They are only slightly less inept than your average architect! No offense to any of the architects and engineers on the forum here).

 

Turns out the 02 sensor thread is M18 1.5 (pitch). The correct drill bit size for this tap is 16.5mm or 21/32 inch. Both the tap and drill bit can be purchased from McMaster Carr, not the least expensive source, but the quickest.