What is the bolt w/nut called thats inside the strut tower (in the middle)?

Everytime I try to tighten the nut the bolt moves with it on my drivers side. WTF?! I got major ratlle when I drive slow because of it. Help.

 

if ur under the hood,the middle bolt is connected to the strut.the three bolts around it are the strut mount.ull need to replace the strut and make sure the mount is still good..how long has this been happening?..heres a link to help u out..2 choices of struts..http://store6.yimg.com/I/racerwheel_1801_208068354then blues http://store6.yimg.com/I/racerwheel_...0422087..heres the mounts link _md.jpg..hope this helps,another pic i found http://www.partsamerica.com/product_...MON/902989.jpg

 

as he said the center bolt is the strut itself.
chances are the strut is worn and should be replaced
I sell struts

 

Nissan calls it an insulator. It is supposed to be bonded to the black metal cap with the 3 nuts and not turn. Like the others have said, the nut you see is on the shaft of the strut itself. The strut rod is shaped like a letter D where it goes through the insulator. The insulator being bonded to the metal shell lets you loosen the nut which, at the moment you can't. My local Nissan dealer charged me $42 for an insulator. To change it, you have to take out the strut, so you may want to replace the strut while you are at it.

 

Try an impact wrench. If you can't get a mechanic to tighten it with an impact wrench, you are going to have to get curved handle box end on it and secure the middle portion with a vise grip wrench