I am not sure to either of your questions. Sorry. I bought them off Ebay a few years ago for a project & never used them. They are not bendable though so they are pretty strong.
The reason for concern is, some base metals include nickel, and some people are nickel sensitive. Because I have nickel sensitive customers, I am unable to bid on metals that I do not know the content of. I'm sure they will work fine for someone who does not have the nickel sensitivity issue.