In scenarios such as electronic equipment, toys, and models—where strict requirements for surface flatness and safety apply—"concealment" and "anti-theft performance" of screws become key needs. As a specialized fastener complying with Chinese National Standards, the countersunk-head inner hexagon machine screw - GB2673, with its threefold advantages of "countersunk-head concealment + inner hexagon anti-theft + machine thread adaptability", perfectly solves problems like "exposed screws affecting appearance" and "loosening caused by unprofessional operation". It has become a preferred fastening solution in the electronic, toy, and model industries, and is also suitable for public equipment scenarios due to its anti-theft feature.
I. Product Definition: A Concealed Anti-Theft Fastener Under National Standard Specifications
The countersunk-head inner hexagon machine screw - GB2673 is a machine screw produced in accordance with the GB2673 National Standard. Its core features can be broken down into three aspects:
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"Countersunk head" means the screw head is conical (usually with a 90° conical angle). When tightened, it can be completely embedded in the countersunk hole of the connected component, resulting in a flat surface without protrusions, achieving "concealed fastening".
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"Inner hexagon" refers to the hexagon-shaped groove (6-lobed or 12-lobed) on the screw head, which requires a dedicated hexagon wrench for assembly and disassembly, providing both anti-loosening and anti-unprofessional-disassembly functions.
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"Machine thread" indicates the screw shank is processed with standard machine threads (coarse or fine threads), compatible with prefabricated internal threaded holes. It can be directly screwed in to complete fastening without self-tapping or drilling, and is suitable for hard materials such as metal and plastic.
Its core difference from the pan-head inner hexagon machine screw (GB2672) lies in the "head shape": the pan-head screw remains protruded after installation, while the countersunk-head screw is completely concealed—making it more suitable for scenarios requiring high surface flatness (e.g., mobile phone casings, toy panels). Additionally, the combination of the inner hexagon groove’s anti-theft feature and the countersunk head’s concealment ensures it not only avoids exposed screws affecting appearance in models and public electronic equipment but also prevents malicious disassembly or incorrect operation.
II. Standard Specifications: Core Technical Requirements of GB2673
As the exclusive national standard for countersunk-head inner hexagon machine screws, GB2673 is tailor-made for "concealed fastening" scenarios, with strict regulations on dimensional accuracy, mechanical properties, and surface treatment:
Dimensional Accuracy
Centered on the nominal diameter (common specifications: M1.4-M8), it strictly defines the countersunk head angle, head diameter, and hexagon groove depth. For example, for an M3 screw: the tolerance of the countersunk conical angle is ±1°, the maximum head diameter is ≤5.6mm, and the hexagon groove depth is ≥1.1mm—ensuring complete embedding in the countersunk hole and a flat surface after tightening. The thread accuracy of the shank is Grade 6g, ensuring no jamming when fitting into internal threaded holes and guaranteeing assembly efficiency.
Mechanical Properties
Grades are classified by material: carbon steel materials must meet Grade 4.8 (tensile strength ≥400MPa), and stainless steel materials (e.g., 304) must have a tensile strength ≥500MPa—ensuring no breakage or thread stripping in light-load scenarios such as electronics and toys. It also requires sufficient connection strength between the head and shank: the head must not fall off during torque testing to avoid fastening failure.
Surface Treatment
The national standard recommends processes such as galvanizing (white zinc, colored zinc), passivation, and black oxide coating. The galvanized layer thickness must be ≥5μm, and it must pass a 48-hour salt spray test without rusting—suitable for humid environments (e.g., bathroom electronic equipment). Passivation treatment is applied to stainless steel materials to enhance corrosion resistance, meeting hygiene and environmental requirements (compliant with RoHS standards) for toys and models.
These specifications ensure interchangeability of GB2673 screws produced by different manufacturers, reducing supply chain costs and providing a clear basis for user selection.
III. Structural Advantages: A Trinity of Concealment, Anti-Theft, and Anti-Loosening
The structural design of the countersunk-head inner hexagon machine screw - GB2673 focuses on "aesthetics, safety, and practicality", with three prominent advantages:
1. Concealment and Protection of the Countersunk Head
The conical head fits precisely with the countersunk hole, resulting in a flat surface after installation. This not only prevents exposed screws from scratching hands (especially suitable for children’s toys) but also enhances the overall aesthetics of the product—for example, model casings and electronic equipment panels appear more refined without protruding screws. Additionally, the tight fit between the countersunk head and the countersunk hole reduces the entry of moisture and dust, extending the service life of internal components.
2. Anti-Theft and Anti-Loosening of the Inner Hexagon
The multi-lobed hexagon groove ensures a tight fit between the wrench and the screw, preventing slippage during force application. Its anti-loosening effect is superior to cross or slotted screws, making it suitable for vibrating scenarios such as electronic equipment transportation. The requirement for a dedicated wrench prevents children from disassembling internal toy parts or unprofessional personnel from tampering with public electronic equipment (e.g., charging pile control panels), improving safety.
3. Adaptability Flexibility of Machine Threads
The standard machine threads on the shank are compatible with various internal threaded holes, eliminating the need for additional drilling. It enables quick assembly in scenarios such as electronic circuit boards, toy plastic parts, and model metal brackets. With high thread accuracy, it resists thread stripping even after repeated assembly and disassembly, meeting the needs of model debugging and electronic equipment maintenance.
IV. Application Scenarios: An "Exclusive Fastener" for Electronics, Toys, and Models
With its "concealment + anti-theft + adaptability" features, the countersunk-head inner hexagon machine screw - GB2673 is precisely suited for multiple fields:
Electronics Industry
For fixing mobile phone middle frames, tablet casings, and smart watch panels, M1.4-M2.5 screws are commonly used. The countersunk head ensures a flat casing surface without affecting hand feel; the inner hexagon’s anti-theft feature prevents component damage from unprofessional maintenance, meeting the precision assembly needs of electronic equipment.
Toy and Model Industry
For assembling children’s building blocks, remote-controlled toys, and Gundam models, M2-M3 Stainless steel screws are preferred. The concealed countersunk head avoids scratching children, complying with toy safety standards; the inner hexagon’s anti-disassembly feature prevents children from accessing internal motors and batteries. Meanwhile, its resistance to thread wear after repeated assembly makes it suitable for model debugging.
Public and Small-Scale Equipment
For fixing mini charging piles and smart access control panels, galvanized carbon steel screws are used. The concealed countersunk head does not affect equipment appearance; the inner hexagon’s anti-theft feature prevents component theft. The galvanized layer resists moisture, making it suitable for outdoor or semi-outdoor environments and ensuring long-term stable operation of equipment.
V. Usage Precautions
Three points should be noted during use:
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A matching countersunk hole must be pre-processed on the connected component (the diameter and depth of the countersunk hole are determined by the screw specification—e.g., an M3 screw requires a countersunk hole diameter of approximately 5.6mm) to ensure complete concealment of the screw.
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A hexagon wrench of the appropriate specification must be used to avoid damaging the hexagon groove with mismatched tools.
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Tightening torque should be adjusted based on the material: for plastic parts (e.g., toy casings), the torque should be ≤2N?m to prevent cracking; for metal parts, the torque can be moderately increased to ensure secure fastening.
As a specialized fastener under the GB2673 standard, the countersunk-head inner hexagon machine screw, with its features of "concealed fastening, anti-theft and anti-loosening, and multi-scenario adaptability", has become a "versatile fastening tool" in the electronic, toy, and model industries. It not only meets aesthetic and safety requirements but also guarantees assembly reliability, making it an ideal choice for lightweight and precision fastening scenarios.
