The nut is welded to the assembly. The bolt goes up from the bottom into it. That is why you want to get oil on it the threads are exposed through the top and are almost always rust locked. The bracket it all attaches to is sheet metal and is welded to the door. I have posted these pictures for you so you can see what it looks like.
http://community.webshots.com/photo/2112932580102454676VrBuIP
http://community.webshots.com/photo/2818182380102454676IWAfYi