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It should be a clinch stud. Can't remember if it is 10mm or 7/16.
It is stripped inside the top-plate. If you pull the coilover or do it up in the fender-well, clean that stud with some WD40 and a wire brush. Try using a regular nut with washer/lock washer instead of a nylock or c-lock and it should bite and tighten up. Removing it in the future when the threads corrode again will be a bitch though. This will not work if the nut was cross-threaded and the stud threads are messed up though.
Thank you guys for all the help and suggestions. Seems like I am going to have to take it out eventually and get the bolt replaced in order for the nut to go in. I will probably just drive it around like this, I don't see no harm as long as I don't go crazy off roading. The two top nuts are holding it in place somewhat and the two bottom studs with the control arm bolt are holding it so I don't think it would be falling out anytime soon lol. Will keep you guys updated though. Btw opinions on the coilover, they are definitely stiffer but I don't a whole lot a difference in the travel. Bumps and cracks still feel the same.