According to the nominal thickness of the hexagon nut is divided into I, II and thin three types. Nuts above grade 8 are divided into two types: type 1 and type II. Type I hexagon nuts are the most widely used, and type 1 nuts are divided into A, B, C three levels, of which A and B level nuts are suitable for small surface roughness and high precision requirements of machines, equipment and structure, while C level nuts are used for rough surface and low precision requirements of machines, equipment or structure; Type 2 hexagon nut thickness is thicker, more often in the need to assemble and disassemble the occasion.