Spring Hanger Studs???

Those are the proper bolts and nuts to use. Picey lil'buggers. Have you tried the dealer?

The issue with store brought bolts and nuts may be with the bolts head. Notice the E-bay ad, the bolts have a small rounded head that is a bit shorter. Also, right under the head, the shaft of the bolt is a solid - unthreaded shaft. This is pressed fitted into the hanger so it doesn't back outwards or rotate.

While it is possible to use a grade 8 or better bolt in place of there, I have not done so myself and a fitmet would be in order to make sure the bolt head dosen't contact the springs end.

Lock tight them on.