It made of 304 Stainless Steel which is corrosion and stain resistant.
Economical Ear Nuts, Friction Earring Backs for Stud Earrings, ideal for fashion jewelry earring designs.5mm thick, hole: 1mm.304 Stainless Steel Ear Nuts, Friction Earring Backs for Stud Earrings, Stainless Steel ColorSize: about 4mm wide, 5mm long, 2. 304 Stainless Steel Ear Nuts.