Ningbo Zhongli Bolts Manufacturing Co., Ltd. founded in 2003, is a professional manufacturer of high-strength fasteners in different specifications for various models, which is covering an area of about 10,000 square meters, registered capital of 1500,000 RMB, with the total annual productivity of 8,000 tons per year. The company has set up several sales branches in different provinces in China. Meanwhile, the company’s products are exported to Europe, USA, Middle East, Africa, Southeast Asia and other regions.
In numerous fields such as mechanical manufacturing, construction engineering, and the automotive industry, hexagonal bolts are one of the most fundamental yet crucial fasteners. A wrong selection of a single bolt may lead to equipment shutdown, structural hazards in buildings, or even safety accidents. In 2026, as industrial manufacturing moves towards high-end and intelligent development, and as the requirements for reliability and compliance in various industries continue to rise, the selection of hexagonal bolts is no longer simply a matter of “following the map”, but rather requires precise decision-making based on multiple factors such as material performance, standard specifications, and scene demands.
I. Anchoring Standards: Understanding the “Identity Description” of Bolts
1. Core standard system: From national standards to international common norms
In 2026, the core standard for the production and application of hexagon bolts in China will still be “GB/T 5782-2016 Hexagon Head Bolts”. This standard is applicable to coarse-threaded common thread hexagon head bolts with thread specifications ranging from M1.6 to M64 and performance grades from 4.8 to 12.9. It serves as the “universal language” in fields such as mechanical manufacturing, construction, and automobiles. In addition, for high-strength and special-scenario bolts, there are specialized standards such as “GB/T 1228-2024 High-Strength Large Hexagon Head Bolts for Steel Structures”. The new version of the standard, which will be put into use in April 2025, has added the M36 specification and the design of external chamfered washers, and has stricter requirements for materials and processes.
In international projects, engineers also need to be familiar with international norms such as ISO 4017 (International Organization for Standardization Standard for Hexagonal Head Bolts), ASME III (American Society of Mechanical Engineers Standard for Nuclear Power Plants), and RCC-M (French Code for the Design and Construction of Mechanical Equipment for Pressurized Water Reactor Nuclear Islands). For example, bolts in nuclear power projects must comply with RCC-M or ASME III standards, while bolts for medical equipment need to meet the requirements of ISO 13485 medical Device quality management system.
2. Key parameter decoding: Dimensional accuracy determines connection reliability
The various parameters in the standard are the core guarantee of bolt quality. Engineers need to pay close attention to the following indicators when selecting the type
Thread specification: The standard clearly stipulates that the thread profile Angle is 60°, and the pitch must comply with the requirements of “GB/T 196 Basic Dimensions of Common Threads”. The deviation of the thread diameter must be controlled within ±0.1mm to ensure precise fit with the nut. For high-precision equipment, it is recommended to use thread gauges for individual inspection. For small-sized bolts below M10, automated optical inspection equipment can be used to enhance accuracy.
Head dimensions: The tolerance of the edge width (s) of the hexagonal head is ±0.2mm, the tolerance of the head thickness (k) is ±0.15mm, and the perpendicularity of the head top surface to the screw axis is ≤0.5mm/100mm. The size of the head directly affects the torque transmission of the wrench. If the size exceeds the tolerance, it can easily cause the wrench to slip or the head to break. In production, the cold heading die needs to be calibrated regularly, and key dimensions should be randomly inspected using a three-coordinate measuring instrument.
Rod section dimensions: The rod section diameter (d) is manufactured according to the tolerance grade g6 or h8, and the rod length (l) tolerance is set based on the length range. For example, when l≤100mm, the tolerance is ±0.3mm, l> ±0.4mm when 100mm. The bending degree of the rod part should be no more than 0.2mm/100mm to prevent the bolt holes from not being smoothly inserted during installation. Under the demand for high precision, the processing of the rod part can adopt grinding process instead of turning to improve dimensional stability.
Ii. Material Selection: The “sinews and bones” that match the scene
1. Mainstream material classification: From carbon steel to special alloys
In 2026, the mainstream materials for hexagonal bolts will be divided into two major categories: carbon steel and stainless steel. For extreme scenarios, alloy materials will also be used.
Carbon steel material: It offers high cost performance and is the most widely used choice in the industrial field. It can be further classified into different grades such as Q235, 45 # steel, and 35CrMo. Q235 steel is suitable for 4.8 grade common bolts and is often used in scenarios where strength requirements are relatively low. Steel No. 45 can achieve a strength of grade 8.8 through heat treatment and is widely used in the mechanical and construction fields. 35CrMo is a commonly used material for 10.9 and 12.9 grade high-strength bolts, featuring excellent tensile strength and toughness, and is suitable for heavy-load and vibrating environments.
Stainless steel material: It has excellent corrosion resistance, with 304 and 316L being the mainstream. 304 stainless steel is suitable for ordinary damp environments, such as food processing equipment and outdoor architectural decoration. 316L stainless steel, due to the addition of molybdenum, has stronger corrosion resistance and can be used in high salt spray and high corrosion scenarios such as Marine vessels and medical equipment.
Alloy material: For extreme scenarios such as nuclear power and aerospace, special materials like nickel-based alloys and titanium alloys are used. These bolts possess extremely high tensile strength, high-temperature resistance, and corrosion resistance, meeting the connection requirements of key components such as nuclear reactor peripheral equipment and aero engines.
2. Performance grade matching: A balance between strength and toughness
The performance grade of hexagonal bolts directly reflects their mechanical properties. Common grades range from 4.8 to 12.9. The first digit of the number represents 1/100 of the tensile strength, and the second digit indicates the ratio of the yield strength to the tensile strength. For example:
Grade 4.8: Tensile strength ≥400MPa, yield strength ≥320MPa, suitable for common load scenarios, such as furniture assembly and simple mechanical fixation.
Grade 8.8: Tensile strength ≥800MPa, yield strength ≥640MPa. It is the mainstream choice in the industrial field and can meet the demands of most scenarios such as mechanical manufacturing and building structures.
Grade 10.9: Tensile strength ≥1000MPa, yield strength ≥900MPa, suitable for heavy-load and vibrating environments, such as automotive engines, large cranes and other equipment.
Grade 12.9: Tensile strength ≥1200MPa, yield strength ≥1080MPa. It is one of the highest strength bolt grades at present and is often used in extreme scenarios such as aerospace and nuclear power.
When engineers select the type, they need to calculate the required tensile strength and yield strength of the bolts based on the actual load to avoid cost waste due to “overkill” or safety hazards caused by “insufficient strength”. At the same time, attention should be paid to the toughness of the material to avoid brittle fracture due to excessive hardness. For example, for 12.9 grade bolts, it is necessary to ensure that the impact toughness is ≥27J (at room temperature).
Iii. Scene Adaptation: Precise Selection from General to Special
1. Construction field: The “ballast stone” of structural safety
In construction projects, the selection of hexagonal bolts should focus on strength, corrosion resistance and durability.
Steel frame structure and bridge construction: High-strength carbon steel bolts should be selected, such as 10.9S grade high-strength large hexagon head bolts for steel structures (conforming to the “GB/T 1228-2024” standard), with tensile strength reaching 1040-1240N/mm². The hardness of the matching nuts should not be lower than that of the bolts, and the hardness of the washers should be between 329-436HV10. In damp environments such as bridge construction, bolts need to undergo anti-corrosion treatments like hot-dip galvanizing and Dacromet, and the salt spray protection time should reach over 1,000 hours to ensure long-term stable operation.
Civil buildings and decoration: For the connection of components in ordinary civil buildings, 8.8 grade carbon steel bolts can be selected. However, for outdoor decoration, curtain wall installation and other scenarios, it is recommended to use 304 stainless steel bolts, which take into account both aesthetics and corrosion resistance. For instance, the bolts for fixing the roof structure need to have good wind pressure resistance, while the fixation of exterior wall materials should take into account the anti-corrosion requirements when exposed to wind and rain for a long time.
2. Mechanical Manufacturing: The Stable “joints” of Equipment
The field of mechanical manufacturing has extremely high requirements for the precision, strength and anti-loosening performance of bolts.
General machinery: such as machine tools, water pumps and other equipment, 8.8 grade carbon steel bolts can be selected, used in combination with spring washers and flat washers. The installation process is simplified through pre-assembled hexagon socket combination bolts, and at the same time, the elastic deformation of the spring washers offsets the stress relaxation caused by vibration. For high-precision machine tools, bolts with higher tolerance grades should be selected, and the diameter of the shank should adopt g6 tolerance to ensure connection accuracy.
Heavy machinery and mining equipment: Such equipment is constantly exposed to heavy loads and vibration environments. Therefore, high-strength bolts of grade 10.9 or 12.9 should be selected. Alloy structural steels such as 35CrMo and 42CrMo should be given priority in terms of material, and advanced anti-corrosion treatments such as Dmet and Teflon should be adopted. For instance, the connecting bolts of the excavator’s bucket need to withstand tremendous impact forces. The high strength of 12.9 grade bolts can effectively prevent the risk of breakage.
3. In the automotive and new energy sectors: Balancing lightweight and reliability
In 2026, the demand for bolts in the new energy vehicle industry will show a trend of lightweighting, high strength and high corrosion resistance
For traditional fuel vehicles, 10.9 grade high-strength bolts should be selected for key parts such as the engine and chassis, while anti-loosening bolts, such as hexagon socket bolts with nylon locking rings, should be used for vibration parts like the transmission and suspension system. The connection of the body sheet metal can use 8.8 grade carbon steel bolts, and the connection strength can be enhanced by spot welding process.
For new energy vehicles, the connection bolts of battery packs need to have high strength, high insulation and corrosion resistance. They are often made of 316L stainless steel or carbon steel bolts treated with Teflon coating, and at the same time, they must meet the IP67 water and dust resistance grade requirements. For components such as motors and electronic control systems, lightweight high-strength aluminum alloy bolts should be selected to ensure strength while reducing the overall vehicle weight.
4. Special Scenarios: Customized solutions for extreme environments
In the fields of nuclear power and medical care: Bolts used in nuclear power projects must comply with nuclear-grade fastener standards, such as RCC-M or ASME III. The materials are mostly nickel-based alloys, featuring high-temperature resistance, radiation resistance, and corrosion resistance. Bolts in medical equipment must comply with the ISO 13485 standard, be biocompatible, and avoid causing harm to the human body. They are often made of 316L stainless steel and have undergone passivation treatment.
In the fields of Marine and chemical engineering: Bolts for Marine vessels and offshore platforms must have extremely strong resistance to salt spray corrosion. 316L stainless steel bolts are the basic choice, and titanium alloy bolts can be used in extreme scenarios. Bolts in the chemical industry need to be resistant to strong acid and alkali corrosion. Carbon steel bolts or Hastelloy bolts with Teflon coating are ideal choices, and the salt spray protection time can reach more than 2000 hours.
Iv. Quality Control: Full-process management from selection to installation
1. Supplier Evaluation: Select partners with core capabilities
In 2026, enterprises in the hexagonal bolt market can be classified into three categories. Engineers need to select appropriate suppliers based on project requirements
Standard parts bulk suppliers: such as Dongguan Aozhan Screw Co., LTD., have the advantages of large production capacity and strong price competitiveness. They can meet the bulk purchasing needs of large-scale projects such as metro projects and power engineering. Their products usually comply with national standards, German standards, etc., and have stable quality.
Non-standard customization suppliers: Such as Dongguan Yuyang Hardware Products Co., LTD., specializing in small-batch non-standard customization, with a fast response speed and the ability to quickly deliver personalized products, suitable for the special needs of industries such as automation equipment and 5G communication base stations.
Comprehensive service providers: Such as Dongguan Ningli Hardware Products Co., LTD., possess the full-process capability from standard parts supply to non-standard customization. Meanwhile, they have a complete quality control system. Their products have passed the ISO 9001-2000 quality certification and can meet the compliance requirements of overseas engineering projects and domestic strong regulatory scenarios.
2. Inspection and testing: Ensure that the products meet the standard requirements
When engineers receive bolts, they need to conduct strict inspection and testing:
Visual inspection: Check whether there are cracks, burrs, rust and other defects on the surface of the bolts, and whether the head size and thread profile meet the standards.
Mechanical property testing: The tensile strength and yield strength of the bolts are tested by a tensile testing machine, and the impact toughness is tested by an impact testing machine to ensure that they meet the requirements of the corresponding performance grades.
Anti-corrosion performance testing: Salt spray tests are conducted using a salt spray test chamber to evaluate the anti-corrosion capability of the bolts. For instance, the salt spray time for bolts coated with Dacromet should be ≥1000 hours.
Compliance verification: For scenarios with strict supervision, it is necessary to check the quality certificates and certification certificates provided by the suppliers. For example, nuclear power bolts need to provide nuclear-grade qualification certificates, and medical equipment bolts need to provide ISO 13485 certification documents.
3. Installation and Maintenance: Details determine service life
The correct installation and maintenance of bolts are the key to ensuring their long-term stable operation
Torque control: Use a torque wrench to apply the tightening torque as per the design requirements to prevent bolt breakage due to excessive tightening force or loose connection caused by insufficient tightening force. For instance, the recommended tightening torque for 8.8 grade M16 bolts is approximately 200-250N·m.
Anti-loosening measures: In a vibrating environment, anti-loosening bolts should be used or anti-loosening washers and lock nuts should be installed to prevent the bolts from loosening due to vibration. Common anti-loosening methods include friction anti-loosening (such as spring washers, nylon lock rings), mechanical anti-loosening (such as cooved pins, stop gaskets), and permanent anti-loosening (such as welding, bonding).
Regular inspection: For bolts in key equipment and building structures, it is necessary to regularly check their tightness and corrosion conditions. If any loosening or rusting is found, they should be replaced promptly to prevent accidents caused by bolt failure.
V. Future Trends: New Opportunities for Intelligence and Lightweighting
In 2026, the hexagonal bolt industry is moving towards intelligence and lightweighting. Engineers need to pay attention to the following trends:
Intelligent production: An increasing number of enterprises are introducing industrial robots and digital inspection equipment to achieve full-process automation in bolt production, enhancing product precision and consistency. For instance, by optimizing the parameters of cold heading dies through big data analysis, the tolerance of the head size can be controlled within 80% of the design value.
Lightweight materials: With the development of industries such as new energy vehicles and aerospace, the application of lightweight bolts made of high-strength aluminum alloys and titanium alloys is gradually increasing, effectively reducing weight while ensuring strength. For instance, the weight of aluminum alloy bolts is only one third that of carbon steel bolts, which can significantly reduce the overall weight of new energy vehicles.
Green and environmentally friendly processes: Environmentally friendly surface treatment processes have become mainstream. Processes such as Dacromet and chromium-free passivation are gradually replacing traditional galvanizing processes, reducing heavy metal emissions and meeting national environmental protection policy requirements.
Media Contact
Company Name: Ningbo Zhongli bolts manufacturing Co., Ltd.
Contact Person: David Dai, Sales
Email: Send Email
Phone: +86-574-86587617, +8615257861940
Address:Tiangu Industrial Zone, Jiulonghu Region, Zhenhai District
City: Ningbo
State: Zhejiang
Country: China
Website: https://www.cnzyl.com/