Hicarer 12 Pieces Locking Magnetic Jewelry Clasp Round Necklace Clasp Closures Bracelet Extender for Jewelry Making (Gold, Silver)

Is this clasp light enough to use on dainty gold necklaces? Some clasps are quite heavy and pull the necklace down on the back on the neck. Thank you.

Do these contain nickel?

What are these made of, sterling, copper what?

Will they rust if they get wet?