This part of GB/T 6187 specifies the type, size, technical conditions and marks of type 2 all-metal hexagon flange lock nuts. This part applies to type 2 all-metal hexagonal flange lock nuts with thread specifications M5~M20, performance grades 8, 10 and 12, and product grades A and B. Grade A is used for D≤16 mm; Grade B is used for nuts with D>16 mm.