Bolts: mechanical parts and cylindrical threaded fasteners with nuts. A class of fasteners consisting of two parts of the head and the screw (a cylinder with an external thread). It is necessary to fit with the nut for fastening and connecting two parts with through holes. This form of connection is called a bolt connection. If the nut is screwed down, the two parts can be separated, so the bolt connection is a detachable connection. 

According to the way of connecting force, it is divided into ordinary and reamed holes. According to the shape of the head, there are six horns, round heads, square heads, countersunk heads and so on. The six corners are the most commonly used. The general sinking head is used where the connection is required. 

According to the type of thread, it can be divided into two types: coarse teeth and fine teeth. The bolts are classified into 3.6, 4.8, 5.6, 5.8, 8.8, 9.8, 10.9, 12.9, of which 8.8 (8.8 grade) bolts are made of low carbon alloy steel or medium carbon steel and are treated by heat treatment (quenching + tempering), all known as high strength bolts, below 8.8 level (excluding 8.8 level) general name bolts. 

According to the production accuracy, ordinary bolts can be divided into three grades: A, B and C. A and B grade are refined bolts, and C grade is coarse bolts. For connection bolts of steel structure, except for special indication, they are generally coarse C grade bolts. Different processing methods are different, usually corresponding to the following processing methods: A, B bolt rods formed by the lathe, smooth surface, accurate size, the material performance grade is 8.8, the production and installation of complex, high price, rarely used, C bolts are made of unprocessed round steel, the size is not accurate enough, The material performance grade is grade 4.6 or 4.8. The shear connection is large in deformation, but easy to install and low in production cost. It is usually used for temporary connection when tensile connection or installation. 

There are many kinds of bolts. Each person may call different ways. Someone calls a screw. Someone calls a bolt and someone calls it a fastener. Although there are so many names, they all mean the same thing. They are all bolts. The bolt is a general statement of the fastener. The bolt is a tool that uses the physical and mathematical principles of the circular rotation and friction of the inclined plane of the object to step by step to fasten the utensils. 

Bolts are indispensable in daily life and industrial production. Bolts are also known as industrial meters. It can be seen that the use of bolts is widely used. The applications of bolts include electronic products, mechanical products, digital products, power equipment, mechanical and electrical products. Bolts are also used in ships, vehicles, water conservancy projects, and even chemical experiments. It's a bolt in a lot of places. Especially the precision bolts used on digital products. DVD, miniature bolts used for cameras, glasses, watches and electronics; general bolts for television, electrical products, instruments, furniture, etc.; for engineering, construction, and bridges, large bolts and nuts are used; traffic appliances, aircraft, tramcars, cars, etc. are used for bolts and bolts. Bolts play an important role in industry. As long as there is industry on the earth, the function of bolts is always important. 

The general sunk head is used in the place where the surface is smooth and not protruding after the connection is required, because the countersunk head can be screwed into the part. The round head can also be screwed into the part. The tightening force of the square head can be larger, but the size is very large. In addition, in order to meet the need of locking after installation, there are holes in the rod with holes in the head. These holes can make the bolts not loose until they are vibrated. Some bolts without thread should be thin, called thin waist bolts. This kind of bolt is beneficial to the connection of the variable force. The steel structure has special high-strength bolts, the head will be bigger and the size will be changed. In addition, there are special uses: T groove bolts, the most used machine tool clamps, the shape is special, the sides of the head should be cut off. Anchor bolts are used to connect machines to the ground and have many shapes. U - shaped bolts, as mentioned above. Wait. There is also a special stud for welding, with one thread on one end, which can be welded on the part and the other side directly screwed the nut. 

Used in common and hinged holes. Ordinary main bearing axial force can also bear the required lateral force. The bolts used for reaming holes should be matched with the size of holes to be used when transverse forces are applied. 

According to the relevant standards, the performance grade of bolt is divided into more than 10 grades of 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, of which the 8.8 and above bolts are made of low carbon alloy steel or medium carbon steel and are treated by heat treatment (quenching and tempering), commonly known as high strength bolts, and the rest are commonly known as ordinary bolts. The bolt grade is composed of two parts, that is, the nominal tensile strength of the bolt material and the ratio of yield to strength. 

Bolt detection is divided into two kinds of manual and machine. Artificial is the most primitive and widely used method of uniform detection. In order to minimize the outflow of defective products, the general production enterprise personnel through visual way to treat packaging or delivery of products to be inspected to eliminate bad products (bad including dental injury, mixture, rust, etc.).
Another way is automatic detection of machine, mainly magnetic particle inspection. Magnetic particle flaw detection is the difference between magnetic permeability and magnetic permeability that may exist in the bolt defects (such as cracks, slag, mixing, etc.). The magnetic field in the discontinuous parts of these materials will change after magnetization, and the magnetic flux leakage is formed on the surface of part of the magnetic flux leakage. In order to attract magnetic powder accumulation in the defects of magnetic powder, magnetic marks, under appropriate light conditions, show the position and shape of the defects, and observe and explain the accumulation of these magnetic powders, which has achieved the purpose of eliminating the defective products.
 

Nut is a nut, which is screwed together with bolt or screw to play the part of fastening. All the production and manufacture machinery must use a kind of original piece. There are many kinds of nuts. We often have national standard, British standard, American Standard, and Japanese standard nut. Nuts are divided into carbon steel, high strength, stainless steel, plastic steel, etc. according to the material. According to the product attributes corresponding to different national standard numbers, they are classified into ordinary, non-standard, old national standard, new national standard, American system, British standard and German standard. 

The nut specification sheet is a concrete and detailed way to unify all kinds of nuts and subdivide the specifications of the nuts with tables. There are many kinds of nuts and nuts with different materials. Each type of nut has different specifications, and each screw has its mechanical properties and functions. 

Specification model
Nominal diameter wide flange diameter
3/8 "0.590" 0.433 "0.787"
7/16 "0.750" 0.690 "1"
1/2 "0.750" 0.690 "1"
5/8 "0.940" 0.820 "1.230"
3/4 "1.300" 1.260 "1.770"
7/8 "1.500" 1.200 "2"
M1015mm11mm20mm
M1219mm17.5mm25mm
M1624mm21mm32mm 

The nut is a fastener with internal thread and used in conjunction with bolts. It has internal thread and is used in conjunction with the screw to transmit motion or power.
The size is different, the thread is not divided into different specifications. The general national standard and the German standard are expressed in M (such as M8, M16), the American system and the British system are fasteners (such as 8#, 10#, 1/4, 3/8), and the nuts are the parts connected tightly to the mechanical equipment, and can be connected by the inside thread, the same specification nut and screw. Together, for example, the nut of M4-0.7 can only be matched with the screw of M4-0.7 (in the nut, the inner diameter of the M4 is about 4mm, the distance between the 0.7 fingers and the two threaded teeth is 0.7mm); the American product is the same, for example, the nut of the 1/4-20 can only match the 1/4-20 screw (the inner diameter of the nut is about 0.25 inches, and 20 refers to every inch of the nut. " There are 20 teeth.