I think the only threads were on nuts welded to the inside of the cross member, apparently as it was being manufactured. The holes are .550" diameter, and the bolt has a .465" major diameter.
I can't reach the backside of the hole to replace the nut. The cross member is too thin to be threaded directly.
BTW, only 1 side is lost, so I can compare. But the effect is the same. It gets pretty wobbly, side to side, on the highway.