... also according to customers' reqquirements. 4.Material: super duplex stainless steel, incoloy, incolonel, hastelloy, monel, nimonic etc. 5. Grade ... MaterialCarbon steel,45#,65Mn,stainless steel,brass4.FinishPlain;black; zinc plated(Cr,3+);zinc plated(Cr,6+); hot dipped galvanized; ... quality control from producing to delivery. Stainless steel/galvanized steel spring washer and flat washer,tapper washer