Rust prevention,good meterial,and best quality washer. Support sample provide. hex head self drilling screw with washerMeterial:steel,stainless steelFinish:zinc platedSize:3.5,3.9,4.2,4.8,5.5,6.3Packaging:in bulk or boxesWasher meterial:EPDM,PVC,RUBBER,ECT hex head self drilling screw with washer