The bolt is a metal part in the form of a cylinder with an external thread. At the end is the head necessary to fix the part to the surface. The shape of the head depends on the requirements for the particular connection and installation conditions. Most often, the bolt is mounted using a wrench. Therefore, hexagonal heads are more popular.
Head shapes
- Hex.
- Square.
- Round.
- Cylindrical.
- Conical.
Designation of bolts
For a long time, competing manufacturers used their own standards. This system has undergone a number of major changes, after which all the details began to correspond to certain parameters and marked according to them. This provision was necessary in a rapidly developing industry, in which the lack of standards complicated the production process.
Currently, there are three unified standards according to which markings are applied to bolts for ease of use:
The recommended designation scheme for bolts and screws according to GOST is used in the CIS countries. The requirements of quality standards apply to food, manufactured goods, clothing, etc. ISO is an international metric system adopted in 1964. At the moment, this standard is used in many countries of the world. DIN is accepted and used in Germany. This system has several standards.
Markings on the heads of bolts
The basic information about the bolt can be read on its head, important parameters of the part are indicated there. Designations are required to select a suitable bolt for carrying out various types of work. Of particular importance is the strength of the bolt, which characterizes the operational characteristics of the connection. In the case of the use of bolts in the manufacture of furniture, the minimum strength requirements are put forward to them, which is associated with a small load on the part. If it is necessary to use a threaded connection at complex industrial facilities, higher requirements are put forward to the bolt.
Also, the stamp of production on which the part is made is applied to the bolt. Additionally indicate the direction and nature of the thread. Another important stage of marking is the application of information on the composition of the alloy of which the bolt is made: material, steel grade and resistance to chemical components.
Identification of bolts when marking
All bolts except cylindrical bolts with a hole for an Allen key are marked on top of the head. Cylindrical products are marked on the front side. The designation of the bolts is applied in the form of symbols deepened in the head or convex signs. Convex marking on the end of the head is rarely applied, most often the signs are deepened. Otherwise, the height of the signs is clearly regulated depending on the diameter of the part.
- Two numbers on the bolt head indicate the strength class of the product. This value is of great importance. It depends on her whether the connection can withstand the load that is necessary in this case. There are 11 strength classes, they are indicated by two symbols with a dot between them. The first designation characterizes the strength of the bolt, and the second - the fluidity of the material from which it is made. At large industrial facilities, in auto and aircraft modeling, this indicator is given special attention. Inconsistency with the marking symbols can cause breakdowns and create emergency situations at the facility. Designation of a high-strength bolt starts from marking 8.8 to 12.9.
- Manufacturer marking - to the leimo with the manufacturer’s symbol, which means that before leaving the production, the part has passed all mandatory quality checks and meets the parameters applied to the part. The absence of a manufacturer’s brand is possible, but may be a sign that the part does not meet quality standards.
- Thread designation. It is mandatory to apply information to the bolt head with a left-hand thread. It is indicated by an arrow. Connections with right-hand threads are not marked separately.
- Letters on the head. These symbols may indicate the metal from which the bolt was made and the grade of steel. Designations A2 and A4 are applied to bolts made from materials resistant to chemicals and air. An underline indicates that the part was made of low carbon Martian steel.
Compliance with GOST
Let's look at what the designation of bolts is in accordance with GOST. All products must comply with state quality standards. Requirements for bolts in Russia and the CIS countries are prescribed in GOSTs. These standards passed to us from the time of the Soviet Union with virtually no change.
There are several GOSTs related to various types of bolts. They indicate not only the requirements for quality, strength, compliance with dimensions and universal parameters, but also the designation scheme of parts during marking and the indication of a particular type of bolt in the drawings.
What is indicated in the standards?
For such products, there are a number of requirements and designations. The bolts according to GOST must comply with all prescribed quality standards. In addition, the documentation contains layouts that this type of product must comply with. The drawings, attached to state quality standards, indicate the design features of the bolt, the legend and the layout of the symbols for marking.
Basic requirements in accordance with GOST
- The parts should be completely free of traces of metal corrosion, major defects and cracks. The presence of the latter means that the product does not meet the quality standard.
- Stamping cracks are allowed on the surface of the part, provided that the length of the crack is less than the diameter of the bolt, and the width and depth are not more than 4% of the diameter of the bolt. Otherwise, the product cannot comply with the state quality standard and should be discarded.
- According to GOST, there may be rolled bubbles on the bolt, but their size cannot be more than 3% of the diameter of the product.
- A bolt with lacerations that come into the thread or the support part is also rejected.
- According to the quality standard, products having defects at the end of the head may be suitable provided that the defect does not exceed the circumference above the limit value.
- A slight point change in the color of the alloy in the form of rowaniness is allowed.
Quality control
All products are controlled by two parameters: visual compliance with the standard and metallographic examination. During visual quality control, the product is inspected for deviations from the state standard in size and diameter, the presence of mechanical damage and defects, as well as the presence of corrosion changes. Metallographic evaluation involves magnetic research. For a more detailed study of the composition of the part, a metal etching method can be used. These methods make it possible to accurately determine the amount of impurities in the alloys and the nature of the material from which the product was made. If the part does not meet the standards, it is rejected.
Decoding scheme of bolt symbols
The symbol of the bolt is presented in the form of a long list of numbers and letters, each of which indicates a specific product parameter. This information is indicated on the manufacturer’s factory packaging and provides comprehensive information about the part.
At first glance, it might seem that deciphering what is indicated on the package is very difficult, but it is not. All designations go in a certain order and characterize a separate product parameter. One of the most commonly used quality standards is GOST 7798-70, it describes the basic parameters of hex bolts. Consider a transcript of an entry using an example.
Product 2M12x1.50LH-5gx50.66.A.047 GOST 7798-70
- Product. In this place they write the name of the part: bolt, screw, stud, etc.
- The quality class is dictated by GOST, therefore, it may not be specified. There are three classes - A, B and C, where the designation A indicates the highest accuracy of the part.
- The number 2 indicates performance. There are only four types of performance. Execution 1 is not specified by default.
- M is a thread type designation. The first letter of its name is indicated: metric, conical or trapezoidal.
- 12 is the diameter of the bolt in millimeters.
- 1,5 - thread pitch, may not be indicated if it is the main thread for a given diameter.
- LH - designation that the left thread on this bolt. If the product is made with the main (right) thread, this will not be indicated.
- 5g indicates which class of precision the thread was cut into. Classes can be indicated by numbers from 4 to 8, where 4 means the most accurate class.
- 50 - bolt length (designation in millimeters).
- 66 - product strength class. On the head of the bolt, these indicators are put with a dot between the numbers. In the symbol, the point is not set.
- A - characteristic used for the manufacture of steel. In this case, it is indicated that the bolt was cast out of automatic steel. The letter C says that the part was made of mild steel. This parameter characterizes the strength class of the bolt. This means that the class is above 8.8.
- 047 indicates the type of coating and its thickness on the product. There are several types of coating - from 01 to 13. In this case, the type of coating is 04, and its thickness is 07 microns.
The symbol of bolt fasteners allows you to most accurately fulfill the requirements for a particular product and design. Compliance with quality standards is the key to successful reproduction of project requirements. Marking that the product complies with GOST allows you to study the properties of the part according to these documents and means its full compliance with standards. Standards according to GOST correspond to other unified systems. To transfer from one system to another, it is enough to use the metric translation table.