Brando 4905 They were originally 3/8-16,you must have hit the original threads that is good. Used to weld on a bigger nut in hopes of not having to take the manifolds off the truck. On tuff ones I sometimes weld on a longer piece of rod at an angle like a lever then heat the iron. It usually wants to move then get tight and will twist off if you force it . The worst is if it leaves a little stub in there,that is hard to drill out,hard to weld onto,and just tuff all around !
