I came across these whilst doing some garage cleaning. They came with the new truck bed I am pretty sure but I don't see where they would go? That hole is threaded, they are steel, a left and a right.
Kind of look like that but not it, bumper bolts to the frame in back. I really do not understand and they were not discussed in the instructions.
They go Inside the rear bottom bed crossmember to reinforce the joint between the stake pockets and the horizontal member, around the hinge area.