It would be hard to find out what grade stainless they are made from, but for the normal person to go into a machine shop and ask for something to be made out of stainless, 9 times out of ten you'll get 304, 304 is a ok grade, but 316L is much better. Another issue that can and will cause rusting in stainless, is the tooling used to brake/bend/work the stainless, it will scratch the surface and leave minute traces of steel in the pores of the stainless, and it will then start to rust, but it is only superficial. Basically any time you touch a piece of stainless with steel (working with it), it will start to rust there.