66 Dart GT HT Whatsitgonnabe?

I'm back. Sorry for the kind of abruptly ended post earlier. I had to go to IKEA with my daughter. Well, she and her friend wanted to go shopping at this place called Lager 157 (translates to Warehouse 157, it has nothing to do with beer ...) which is right next to one of the two IKEA:s in Gothenburg. She could go because I needed a wardrobe for the youngest so we needed to take a trip to IKEA anyway. So while they were shopping, I was hauling the ridiculously heavy PAX boxes on my own. I totally deserve a glass of red now. I'm not kidding, they're 86 pounds. Putting two of them on the roof rack alone is NOT a task for ... anyone.

Anyway, I tried to get the brake calipers mounted too but I couldn't figure out what thread the bolts are. I tried 7/16"-14 but they won't go in easily and I don't want to ruin the thread. 7/16" is really the only bolt size that fits in the holes in the calipers. M12 and 1/2" are both too large and anything smaller (that I have) will go right through the threaded hole.

Can anyone give me a definitive answer here? Original Kelsey-Hayes front disk brakes.