Quality and strong standard type 400 series stainless steel Each pack is professionally heat sealed and labeled by Marine Bolt Supply Offered in convenient small or large quantity packs These standard type 410 stainless steel external tooth lock washers are commonly used with pan or button style head screws. The external teeth bite into the screw providing a tight grip. 400 series stainless steel is the industry standard for these type of locking washers. 400 series provides more strength but slightly less corrosion resistance than 300 series. These are stainless steel but are also mildly magnetic.