A stripped hole is around 10mm, which is the drill size for an M12 thread. I cleaned the hole with a 10mm drill bit, then tapped it to M12 x 1.75.
Then I got an M12 bolt from Bunnings and cut the shank off (I cut it a bit short but that is ok).
I tightened it up with double nuts and then used a die grinder to very slightly enlarge the hole on the exhaust flange so it is easier to put on.


Looks like it will last and won't end up destroying the hole like helicoils do.