How to Correctly Install and Use Low-Strength Hexagon Head Bolts

Basic Preparation Before Installation

1. Inspection of Model Matching

Confirm that the bolt specifications (diameter, length) match the hole diameter and thickness of the connected components. For example, an M4 bolt should be paired with a pre-drilled hole of φ4.2-4.5mm to avoid shear deformation of the bolt during installation due to an excessively small hole diameter. At the same time, verify whether the bolt grade (Grade 4.8 or below) meets the design requirements. It is strictly prohibited to use low-strength bolts as a substitute for high-strength bolts.

2. Surface Pre-Treatment

Clean the threaded surfaces of bolts and nuts to remove oil stains, rust, and burrs—this can be done using a wire brush combined with a neutral cleaning agent to ensure smooth thread engagement. For scenarios where the connected base material is a brittle material such as wood or plastic, pre-drill holes in the base material and install metal sleeves to prevent cracking of the base material when the bolt is driven in.

3. Selection of Suitable Tools

Prioritize the use of torque wrenches or power tools with torque adjustment functions; avoid using adjustable wrenches and other tools that are prone to causing the bolt head to slip. The across-flat width of the hexagon head must strictly match the wrench size (e.g., an M6 bolt corresponds to a 10mm wrench) to prevent "corner slipping" which may damage the bolt head.

Standardized Installation Process

1. Operation During Pre-Tightening Stage

Manually screw the bolt in until it can no longer rotate, ensuring that the initial thread engagement is aligned to avoid oblique force application. For connections that need to pass through multiple layers of components, the nut should be fitted only after the bolt has completely penetrated all layers to prevent thread jamming midway.

2. Key Points for Torque Control

Set a reasonable pre-tightening torque according to the bolt specification: for M3-M4 bolts, the torque is recommended to be controlled at 3-5N・m; for M5-M6 bolts, it is 8-12N・m, with a maximum not exceeding 15N・m (refer to the GB/T 1231 standard for specific values). Over-tightening low-strength bolts can easily lead to thread yield deformation or even fracture. The "progressive tightening method" can be adopted—reach the target torque in 2-3 stages, increasing by 50% each time.

3. Application of Anti-Loosening Measures

In vibrating environments (such as washing machines and small motors), anti-loosening elements must be used in conjunction: a spring washer can be installed under the nut (note that the hardness of the washer must be lower than that of the bolt to avoid scratching the threads), or a nylon insert lock nut can be used. For long-term static connections, a small amount of non-corrosive grease can be applied to the thread surface to facilitate later disassembly.

Precautions for Usage and Maintenance

1. Environmental Adaptability Management

Low-strength bolts (especially unplated low-carbon steel products) are prone to rust in humid environments. After installation, protection measures should be taken based on the scenario: for short-term outdoor use, anti-rust paint should be applied; for indoor high-humidity environments (such as kitchens), bolts with galvanized or Dacromet treatment should be selected, and direct contact with acid-base media should be avoided.

2. Load Monitoring and Replacement

Regularly check whether the connection parts are loose (this can be judged by the alignment of marked lines). If deformation of the bolt head or thread stripping is found, replace the bolt immediately. When replacing bolts at the same connection point, products of the same specification and grade must be used; mixing fasteners of different strengths is prohibited.

3. Disassembly Specifications

When disassembling rusted bolts, do not use brute force to twist them. First, spray a bolt loosener (such as WD-40), let it stand for 5-10 minutes, then use a wrench to unscrew the bolt slowly. If the bolt head breaks, an electric discharge machining (EDM) method or drilling method can be used to remove it, avoiding damage to the threaded hole of the connected base material.

The core principle for the correct installation and use of low-strength hexagon head bolts is "adaptation and moderation": neither should the load exceed their strength limit, nor should their advantages of good toughness and easy assembly be wasted through non-standard operations. In light-duty connection scenarios such as furniture and household appliances, strictly following the above process can extend the service life of the bolts by more than 30% while reducing maintenance costs.

Translation Notes

Term Consistency & Technical Accuracy
- Core terms like "低强度外六角螺栓" (low-strength hexagon head bolts), "4.8 级" (Grade 4.8), and "GB/T 1231 标准" (GB/T 1231 standard) remain consistent with industrial norms. Specialized expressions such as "剪切变形" (shear deformation), "屈服变形" (yield deformation), and "螺纹滑丝" (thread stripping) adopt authoritative mechanical engineering translations to ensure no ambiguity.
- "达克罗处理" is translated as "Dacromet treatment" (a globally recognized anti-corrosion coating process), retaining the original technical term instead of a literal translation to avoid misunderstanding.
Contextual Adaptation of Operational Details
- "溜角现象" is rendered as "corner slipping"—a direct description of the common issue where wrenches slip off hexagon head corners, more intuitive for readers than literal alternatives like "angle sliding".
- "渐进式拧紧法" is translated as "progressive tightening method" with a supplementary explanation ("reach the target torque in 2-3 stages..."), clarifying the operation steps for users unfamiliar with the technique.
Sentence Structure Optimization
- Long procedural clauses (e.g., surface pre-treatment steps) are split using em dashes and bullet points to align with English technical writing conventions, enhancing readability. For example, "清理螺栓与螺母的螺纹表面…… 防止基材开裂" is structured into two clear parts: cleaning method and preventive measures for brittle materials.
- Passive voice (e.g., "should be paired with", "must be used", "can be adopted") is strategically applied to emphasize operational requirements, focusing on "what needs to be done" rather than the operator, which is standard in installation guides.
Preservation of Quantifiable Data
- Specific parameters (e.g., "φ4.2-4.5mm", "3-5N・m", "5-10 minutes") are retained exactly to maintain the guide’s practical value. Units like "N・m" (newton-meters) use international standard symbols, ensuring consistency across global markets.

How to Correctly Install and Use Low-Strength Hexagon Head Bolts