this is a carbon steel made hexagon nuts,it is made of carbon steel material,and surface plates nickel,black nickel,white zinc,black zinc different coating.
Vernickelte Schraubenmuttern, Kontermuttern, Nägel aus Kohlenstoffstahl, rutschfeste Nylon-Sechskantmutter, selbstsichernde Schrauben, Kappe. with high hardness,low temperature resistance,anti-corrosive,anti-rust,wear-resistant those advantages,widely used in home improvement,machine,basic construction and other industries. and this hex nuts insert nylon rings in,make it anti-slip and can locked very tight on screws.