Thats it, its a 3/4 nut. And i think its factory, towing package maybe?

 

Well we weren't able to salvage the bumper so I had to build a new one. It turned out really well and makes me want to make a beefy plate bumper for the front too. We built the rear off the original bumper mounts and I think its stronger than stock which is nice. Sorry no pics...camera broke :/