Well, they aren't on the DOE suspect list. I hate to be dogmatic about this, but if these are for a safety application then your supplier should be able to tell you. If he can't, then you can assume that they are counterfeit. No reputable fastener source these days does not know the original source of bolts.
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Rust never sleeps
Neither should your protection
The only ZB in Fastener Tech. International's identification guide is Z&B General Machine in Penndel, PA. It is kind of an odd design though with the two letters kind of swirled around each other. Could be a different mark.
