A bolt ground really short. Not sure of the size but just use the )2 as a reference and test out a few bolts till you find one with the same thread (overlay the bolt onto the thread on the O2 sensor and if they mesh perfectly you found the bolt) then test out the bolt and see if it screws in . Once you confirm that cut/grind it down so the thread is 1/2" (max) long and reinstall with some anti-seize ont he threads.
