If the nut is smooth and round-headed, it is M30 hexagon socket head screw, and the national standard number is GB70-85. If it is a knurling head, the outer diameter of the nut is slightly larger than 45, but it is also an M30 hexagon socket head screw.
The national standards for hexagon socket head bolts are as follows: MB/T2- 1985, external thread end of fasteners (EQV ISO 4753:1983); MB/T90- 1985 Acceptance inspection, marking and packaging of fasteners (EQVISO 3269:1984);
MB/t196-1981common thread, basic size (diameter1~ 600 mm); MB/t197-1981tolerance and fit of common thread (diameter1~ 355 mm); MB/T 1237-2000 Fastener Marking Method (EQVISO 899 1: 1986).
Extended data:
Basic parameters of hexagon socket head screws;
The specifications of the hexagon socket head screws, the national standard of the hexagon socket head screws is GB70- 1985, and there are many specifications and sizes. Commonly used specifications are 3*8, 3* 10, 3* 12, 3* 16, 3*20, 3*25 and 3.
4*35，4*45，5* 10，5* 12，5* 16，5*20，5*25，6* 12，6* 14，6 * 64。 ?
Hardness of socket head cap screws: socket head cap screws are classified according to the hardness, tensile force and yield strength of screw thread, that is, the level of socket head cap screws and what level of socket head cap screws are. For different products and materials, different grades of hexagon socket bolts are required, and all hexagon socket bolts have the following grades:
Hexagon socket head bolts can be divided into normal strength and high strength according to strength grade. Ordinary hexagon socket head bolts refer to Grade 4.8, and high-strength hexagon socket head bolts refer to Grade 8.8 or above, including Grade 10.9 and Grade 12.9. 12.9 grade socket head cap bolts generally refer to knurled and oiled natural black socket head cap screws.
The performance of hexagon socket head bolts used for steel structure connection is classified as 10 or above, such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc. Among them, bolts of grade 8.8 and above are made of low-carbon alloy steel or medium-carbon steel, and are heat-treated (quenched and tempered);
Commonly known as high-strength bolts, the rest are commonly known as ordinary bolts. The bolt performance grade label consists of two parts of numbers, which respectively represent the nominal tensile strength and yield ratio of bolt materials.