Nyloc Nuts. 5/16" UNF Hex Head Set Screw, Nyloc Nut & Washer Set – A2 Stainless Steel. Includes: 1 × Set Screw, 1 × Nyloc Nut, 1 × Washer. Hex Bolts - UNF. Supplied as a complete set with Nyloc nut and washer.
eBay