Peter
99.9% sure the are a M12 standard metric thread . The threads may be dammaged, clogged with loctite reminants .
Personaly I would run an M12 metric tap through them
A 7/16" UNC bolt would go in there as it is just a tiny bit smaller & of similar thread pitch.
Being M12 metric a 7/162UNC bolt will not provide an adequate grip & will probably strip the thread in the upright when it is torqued up
Dave
Welcome to the club mate.
Would you like an entry in my new magazine .... FUBAR Weekly
