Made of 304 Stainless Steel (no coating outside) which is superior to regular steel and any zinc plated fasteners, provides good strength and corrosion resistance in bad environments. Hard-to-Find Fastener 014973242527 Coarse Hex Serrated Flange Nuts, 5/16-18, Piece Serrated flange nuts are fabricated with a built in serrated washer that resists loosening due to vibration. Serrated flange nuts are fabricated with a built in serrated washer that resists loosening due to vibration UNC Coarse Thread Hex Nuts 5/16-18 (20 Pack) Serrated Flange Hex Nuts, 304 Ghana 5/16-18 Stainless Steel Nuts Hex Drive Size: 1/2; Flange Diameter: 43/64; Overall Height: 9/32 Buy shiyou-5/16"-18 Serrated Flange Hex Lock Nuts Hexagon Nuts, 304 Stainless Steel 18-8, Full Thread, Coarse Thread UNC, Pack of 10 from Canada Package: 10 PCS 5/16-18 Stainless Steel Serrated Flange Hex Nuts The high quality 304 stainless steel provide perfect strength and good corrosion resistance in bad environments like high temperature, cold weather and high humidity areas without the need for time consuming and costly maintenance.