A comprehensive explanation of bolts

Classification
According to the force-bearing mode of the connection, it can be divided into ordinary and reamed holes. According to the shape of the head, it can be divided into hexagonal head, round head, square head, countersunk head, etc. Among them, the hexagonal head is the most commonly used. The countersunk head is generally used in places where connection is required.
The English name of the riding bolt is U-bolt. It is a non-standard part. It is U-shaped, so it is also called U-bolt. There are threads on both ends that can be combined with nuts. It is mainly used to fix tubular objects such as water pipes or sheet objects such as car leaf springs. Because the way it fixes objects is like a person riding on a horse, it is called a riding bolt. According to the length of the thread, it can be divided into full thread and non-full thread. [2]
According to the thread type, it can be divided into coarse thread and fine thread. The coarse thread type is not shown in the bolt logo. Bolts are divided into eight grades according to performance level: 3.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, and 12.9. Bolts above grade 8.8 (including grade 8.8) are made of low-carbon alloy steel or medium-carbon steel and are heat-treated (quenched + tempered), commonly known as high-strength bolts, and bolts below grade 8.8 (excluding grade 8.8) are generally known as ordinary bolts.
Ordinary bolts can be divided into three grades: A, B, and C according to manufacturing accuracy. Grades A and B are refined bolts, and grade C is rough bolts. For connecting bolts for steel structures, unless otherwise specified, they are generally ordinary rough grade C bolts. There are differences in the processing methods of different grades, and the corresponding processing methods are usually as follows: ① The bolt rods of grade A and B bolts are processed by lathes, with smooth surfaces and precise dimensions. The material performance grade is 8.8, which is complicated to manufacture and install, and the price is high, so they are rarely used; ② Grade C bolts are made of unprocessed round steel, the size is not precise enough, and the material performance grade is 4.6 or 4.8. The deformation is large during shear connection, but it is easy to install and has low production cost. It is mostly used for tensile connection or temporary fixation during installation.
Application
Bolts have many names, and each person may call them differently. Some people call them screws, some call them bolts, and some call them fasteners. Although there are so many names, the meaning is the same, they are all bolts. Bolts are a general term for fasteners. Bolts are tools that use the physical and mathematical principles of the circular rotation of the inclined surface of an object and the friction force to gradually fasten objects and parts. [1]
Bolts are indispensable in daily life and industrial production and manufacturing. Bolts are also called the rice of industry. It can be seen that bolts are widely used. The application scope of bolts includes: electronic products, mechanical products, digital products, power equipment, electromechanical mechanical products. Bolts are also used in ships, vehicles, water conservancy projects, and even chemical experiments. Anyway, bolts are used in many places. Especially the precision bolts used in digital products. DVD, miniature bolts used in cameras, glasses, clocks, electronics, etc.; general bolts used in televisions, electrical products, musical instruments, furniture, etc.; large bolts and nuts are used in engineering, construction, and bridges; transportation equipment, airplanes, trams, cars, etc. use both large and small bolts. Bolts have important tasks in industry, and as long as there is industry on the earth, the function of bolts will always be important.
Shape
Generally, countersunk heads are used in places where the surface is required to be smooth and without protrusions after connection, because the countersunk head can be screwed into the parts. Round heads can also be screwed into parts. The tightening force of square heads can be greater, but the size is large. In addition, in order to meet the needs of locking after installation, there are holes in the head and holes in the rod. These holes can prevent the bolts from loosening when vibrated. Some bolts have no threaded bare rods and are called thin waist bolts. This type of bolt is conducive to connection with variable forces. There are special high-strength bolts on steel structures, the head will be larger, and the size will also vary. In addition, there are special uses: T-slot bolts, which are most used on machine tool fixtures, with special shapes, and both sides of the head must be cut off. Anchor bolts are used to connect and fix machines to the ground. There are many shapes. U-shaped bolts, as mentioned above. And so on. There are also special studs for welding, one end has threads and the other end has no threads, which can be welded to parts and nuts can be screwed directly on the other side.
Force mode
Ordinary and with reamed holes. Ordinary ones mainly bear axial forces, and can also bear lateral forces with low requirements. Bolts for reamed holes must match the size of the holes and are used when subjected to lateral forces.
Grade meaning
According to relevant standards, the performance grades of carbon steel and alloy steel bolts are divided into more than 10 grades, including 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, and the rest are commonly known as ordinary bolts. The bolt performance grade number consists of two parts of numbers, which respectively represent the nominal tensile strength value and yield strength ratio of the bolt material. Stainless steel bolts are divided into A1-50, A1-70, A1-80, A2-50, A2-70, A2-80, A3-50, A3-70, A3-80, A4-50, A4-70, A4-80, A5-50, A5-70, A5-80, C1-50, C1-70, C1-110, C4-50, C4-70, C3-80, F1-45, F1-60 according to the type and performance level of steel. The first letter and number represent the group of stainless steel, and the second and third numbers represent 1/10 of the tensile strength.
Bolt detection
Bolt detection is divided into manual and machine. Manual is the most primitive and most commonly used consistent detection method. In order to minimize the outflow of defective products, general production enterprise personnel visually inspect the products to be packaged or shipped to exclude defective products (defective products include tooth damage, mixing, rust, etc.).
Another method is fully automatic detection by machine, mainly magnetic particle inspection. Magnetic particle inspection uses the interaction between the leakage magnetic field at the defective part of the bolt and the magnetic powder. According to the difference in magnetic permeability between the possible defects of the bolt (such as cracks, slag inclusions, mixed materials, etc.) and the magnetic permeability of steel, the magnetic field at the discontinuity of these materials will be distorted after magnetization, forming a leakage magnetic field on the surface of the workpiece where some magnetic flux leaks, thereby attracting magnetic powder to form magnetic powder accumulation at the defective part - magnetic trace. Under appropriate lighting conditions, the defect position and shape are revealed, and the accumulation of these magnetic powders is observed and interpreted to achieve the purpose of eliminating defective products.