18-8 Stainless Steel Hex Nut, Black Oxide Finish, ASME B18.2.2, 5/16"-18 Thread Size, 1/2" Width Across Flats, 17/64" Thick (Pack of 50): Amazon.com: Industrial & Scientific
300pcs) DIN 6926 M8 Self-Locking Hexagon Flange Nuts with Serration A2 Stainless Steel, Ships Free in USA by Aspen Fasteners, ASSP692628: Amazon.com: Industrial & Scientific