All of your stainless bolts from hardware stores are coming from China. Sears, ACE, etc. All the same supplier of bolts. I broke one a grade 8 bolt from Sears, and that was the last time that I bought a cheap bolt.
Here is a good chart that explains the different grades, but all stainless bolts are grade 2 from those stores.
http://www.boltdepot.com/fastener-in...materials.aspx In your application you want at least grade 5 for the serpentine belt. Totally Stainless sells ARP, but they also sell stainless grade 2. Arp website gives you some good information on the metallurgy of their fasteners.
http://arp-bolts.com/p/technical.php#p7TPMc1_4
Jeff
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