Made of high-grade stainless steel with four-sided strands, giving four cleaning edges to handle the toughest jobs. Because each scrubber is made of a single strand of stainless steel, they will not tear or splinter. Will not rust or corrode. 300 series Premium grade manufactured from "300" series high quality stainless steel (18/8). Great for highly aggressive cleaning jobs when scratching is not an issue. "400" series High grade manufactured from less expensive "400" series wire construction. This scrubber has effective properties for the removal of baked-on deposits and other medium duty jobs.