Flapper box thread size
 

Trying to come up with a better way to attach my new flappers to my car.
When taking off the nuts, they of course all snapped off, leaving a smaller
stud behind. My thoughts are to make a threaded sleeve to screw on the
broken studs (which may cause me to enlarge the holes in the flapper) and attach the boxes with a new bolt.
If I can determine what size the old studs are, I can probably make something work. I'd like to figure this out rather than weld them on.

Thanks for any and all input.
Cheers!
Steve

Most likely M6 1.0 thread pitch.

Extending the studs will be a challenge as it will also likely require a spacer on the outside as well. This would be needed to allow the new nut to put clamping force against the outside of the flapper box.

Honestly easier to find a local shop and have them TIG weld some new studs in.
OR a muffler shop might be easier and cheaper. MIG will leave a tiny bit more splatter.

Cooper

Thanks Cooper! I appreciate it! I may be going that route, mig or tig that is,
but I'd like to leave that for a last resort. A friend also suggested drilling the
old studs out and using large sheet metal or self tapping screws.
We'll see.
Thanks again,
Steve

I broke all three off on one side of my car. I drilled and tapped the holes, then put the flapper box on with M6 bolts instead. Not as easy as putting nuts on studs, but I got them in there.