High-Quality Structural Hex Bolt
Ordinary Hex Head Bolts
These bolts are mostly C-grade coarse bolts, with a small number being A and B-grade precision bolts. They have lower strength and are often used as temporary fixations or connections in secondary load-bearing areas.
Core Parameters:
They comply with standards such as GB/T 5780-2000 (partial thread) and GB/T 5781-2000 (full thread). Thread specifications cover M5-M64. Performance grades are mainly 3.6, 4.6, and 4.8. For example, a 4.8 grade bolt has a nominal tensile strength of 400MPa and a nominal yield strength of 320MPa. The material is mostly Q235 carbon structural steel. Grades A and B are precision bolts, offering high dimensional accuracy but also incurring higher costs. Grade C bolts are coarse bolts, with lower machining precision but lower prices; they are the most commonly used ordinary bolts in steel structures.
Applications:
Suitable for temporary fixing of steel structures, such as positioning and connecting steel structural components during construction; also suitable for secondary load-bearing structures, such as small steel structure supports, splicing of non-load-bearing components, and connections in steel structures that can be disassembled later.
High-strength large hexagonal head bolts
These are critical fasteners in the core load-bearing parts of steel structures, often used in connection pairs (containing 1 bolt, 1 nut, and 2 washers). Their performance and precision far exceed those of ordinary bolts.
Core parameters:
Complies with GB/T 1228-2006 standard; performance grades are mainly 8.8 and 10.9. Grade 10.9 bolts have a tensile strength of 1040-1240 N/mm², a yield strength of not less than 940 N/mm², and a Vickers hardness between 312 and 367. Grade 8.8 bolts have a tensile strength of 830-1030 N/mm² and a yield strength of 660 N/mm². They are mostly made of medium carbon steel or alloy steel and require heat treatment to enhance their properties. Some high-strength bolts also undergo galvanizing and other anti-corrosion treatments.
Applicable Scenarios:
Suitable for core load-bearing parts of steel structures, such as steel beam splicing in bridges, node connections in high-rise building steel frame structures, main structure fixing of power transmission towers, and fastening of load-bearing components in large factory steel structures. These scenarios have extremely high requirements for connection stability and safety. High-strength large hexagonal head bolts can achieve precise torque tightening, relying on friction to transfer loads and ensure the overall load-bearing capacity of the structure.
Common Features and Usage Precautions
Common Advantages:
The hexagonal head design facilitates wrench application and tightening, making it suitable for both mechanized and manual installation. Most are used with corresponding hexagonal nuts and washers to improve the sealing and stability of the connection. Some undergo hot-dip galvanizing or other anti-corrosion treatments to extend their corrosion resistance lifespan for outdoor use.
Usage Precautions:
Different grades of bolts should not be mixed. For example, a 10.9 grade high-strength bolt cannot be used with a 4.8 grade ordinary nut. The torque of high-strength bolts must be strictly controlled during installation; the torque wrench error should be within ±5% to avoid over-tightening, which can cause bolt cracking, or under-tightening, which can affect connection strength. Storage should be protected from rain and moisture to prevent thread corrosion and damage. If the bolt and nut are incompatible, their use is strictly prohibited.
