Mystery Nut/Bolt Identification?

[Praxiss454]

Hi all,
Pulled these off of my truck somewhere, and thought enough of it to set them aside. Now I can't remember where they are from or if they're important at all. The only things I've done to the truck recently that I can recall are taking the bed off the frame and putting in new bed wood

Any idea where the hell they're from and what they're for? There are two nuts, two bolts, and those two floating square things that are rounded on one side.