Hexagonal nuts are used in conjunction with bolts and screws to connect and fasten parts. Among them, type I hexagonal nuts are the most widely used. Grade C nuts are used for machines, equipment or structures with rough surface and low precision requirements. Grade A and B nuts are used for machines, equipment or structures with relatively smooth surface and high precision requirements. Type II hexagonal nuts are thicker in thickness m and are often used in occasions where assembly and disassembly are often required. The thickness of hexagonal thin nut m is thinner, which is mostly used when the surface space of the connecting parts is limited.