What is this bolt called, and how do I replace it?

[MWatts]

Went in for inspection today, and they found this bolt to be loose. Its on the drivers side. They called it a control arm bolt? It is visibly smaller than the one on the passenger side. Perhaps someone replaced the drivers side bolt with the incorrect one, and thats why its loose? Either way I need to identify it and replace it to pass inspection.

So once you kind folks help me identify it....how hard is it to replace?
If I take the existing bolt out...will things inside fall part?

Thanks,
Marty