I'm putting a catalytic converter on my truck and need to know if this flange on the o2 sensor can come off it looks like it threads on there but I can't seem to find a way to take it off I was goin to take the flange off of it and weld it to the exhaust pipe. Any suggestions on how to take it off?

 

No that is what bolts to the bung that is welded to the pipe.

They can be found different places online.

Most exhaust pipes most often come with them installed

Unless your just piecing it together from random parts.