Right, the plastic bit that goes into the wing is like a triangle that you twist into the wing so it stays in place.

There's a through hole in the middle of it, no thread or anything.

Inside the bumper is a T piece which has something like a rubber bung which slides into the plastic holder which is on the wing.

The rubber bung has a hole and thread inside it, so that you can run a bolt from the inside of the engine compartment/wing, through the wing holder into the bumper.

If the bolt is freewheeling, that's because the metal thread attached to the bumper has rust-welded itself to the bolt, or, the plastic around it has broken so there's nothing to hold it.

Hope this helps.