I. Structural Understanding: Clarify Core Design and Applicable Scenarios
Before use, it is necessary to first understand the structural characteristics of the flat-head internal-external hexagon blind-hole rivet nut to ensure it matches actual needs. Its head adopts a flat design with a thickness usually ranging from 1-2mm; after installation, the flatness error is ≤ 0.05mm, making it suitable for components requiring flat, non-protruding surfaces, such as instrument panels and automotive interior panels.
The integrated internal-external hexagon drive structure features an internal hexagon hole compatible with H3-H8 specification hexagon socket wrenches, and external hexagon edges matching corresponding-sized external hexagon wrenches. This solves the problem of easy corner slipping with a single drive method, making it particularly suitable for scenarios requiring frequent disassembly.
The blind-hole design means there is no through-hole inside the nut; installation only requires machining a blind hole in the connected component, avoiding the reduction in component strength caused by through-holes. It is suitable for solid plates or closed-cavity components with a thickness of 3-10mm, such as housings of medical devices and sealed boxes of communication equipment.
In terms of materials, three common types are available:
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Galvanized steel: Low cost and good rust resistance, suitable for ordinary dry environments;
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304 stainless steel: High corrosion resistance, suitable for humid, acid-alkaline environments (e.g., outdoor equipment, medical devices);
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Aluminum alloy: Lightweight, suitable for lightweight demand scenarios (e.g., aerospace accessories, new energy vehicle components).
Clarifying structural and material characteristics is the basis for subsequent selection and installation.
II. Selection Guide: Determine Key Parameters Based on Needs
Selection should focus on three dimensions—"connected component characteristics," "service environment," and "assembly requirements"—with emphasis on the following parameters:
(1) Specification Matching: Precise Correspondence Between Hole Diameter and Thread
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Prefabricated hole diameter: Must strictly match the cylinder diameter of the rivet nut. For example, an M4 specification rivet nut is compatible with a φ4.2mm prefabricated hole, and an M5 specification with a φ5.3mm prefabricated hole. An excessively large hole diameter may cause loosening after riveting, while an excessively small one will squeeze and deform the cylinder, affecting thread precision. It is recommended to use a dedicated caliper to measure the prefabricated hole diameter, controlling the error within ±0.1mm.
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Thread specification: Selected based on matching bolts, with common specifications ranging from M3-M8. Attention should be paid to thread precision grades (e.g., Grade 6H for ordinary scenarios, Grade 5H for precision connections). For example, connections of internal brackets in medical devices require M5×0.8 fine threads to enhance anti-vibration performance and prevent bolt loosening.
(2) Material Selection: Adapt to Environment and Strength Requirements
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Dry indoor scenarios (e.g., office equipment, household electronics): Prioritize galvanized steel, which is low-cost and meets basic rust resistance needs;
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Humid, outdoor, or medical scenarios (e.g., outdoor charging piles, surgical instruments): Must select 304 stainless steel, which shows no rust after 48-hour salt spray testing and meets hygiene and corrosion resistance standards;
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Lightweight scenarios (e.g., drone accessories, laptop brackets): Select 6061 aluminum alloy, which is 40% lighter than steel nuts of the same specification and has a strength of over 200MPa.
(3) Length Determination: Reasonable Selection Based on Plate Thickness
The cylinder length of the rivet nut should be 1.5-2mm longer than the thickness of the connected component to ensure sufficient deformation space for the cylinder during riveting. For example, if the connected component has a thickness of 5mm, a model with a cylinder length of 6.5-7mm should be selected. An excessively short cylinder cannot form an effective bite after riveting, while an excessively long one will cause the head to protrude, affecting surface flatness.
III. Installation Steps: Standardized Operation to Ensure Reliable Connection
Specialized tools for installation include: a hexagon socket wrench (matching the internal hexagon specification of the nut), an external hexagon wrench (backup, to prevent internal hexagon corner slipping), a riveting gun (manual or pneumatic, selected based on batch needs), and a caliper (to measure prefabricated holes and post-installation dimensions). The specific steps are as follows:
(1) Pretreatment: Inspection and Cleaning
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Inspect the prefabricated hole of the connected component: Use a caliper to measure the hole diameter and depth, ensuring the diameter meets specifications and the depth is 0.5mm deeper than the cylinder length of the rivet nut (to avoid the cylinder being unable to fit fully due to a shallow blind hole);
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Clean the prefabricated hole and rivet nut: Use compressed air to blow away debris in the hole, and wipe oil stains on the rivet nut surface with alcohol to prevent impurities from affecting riveting tightness. Especially in high-precision scenarios such as medical devices and electronic equipment, cleanliness directly affects connection stability.
(2) Riveting Operation: Step-by-Step Execution with Force Control
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Place the nut: Align the flat end of the flat-head internal-external hexagon blind-hole rivet nut with the surface of the connected component, and slowly insert the cylinder end into the prefabricated hole. Ensure no gap exists between the nut and the hole wall; for slight deviations, gently tap the external hexagon edges to calibrate (violent pressing to avoid cylinder deformation is prohibited);
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Tool adaptation: Prioritize inserting a hexagon socket wrench into the internal hexagon hole of the nut. If corner slipping occurs in the internal hexagon hole, immediately switch to an external hexagon wrench to clamp the external hexagon edges (to avoid further thread damage from continued use);
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Apply pressure: For manual riveting guns, rotate the wrench at a constant speed while applying axial pressure. For pneumatic riveting guns, adjust the pressure to 8-15kN (12-15kN for steel nuts, 8-10kN for aluminum alloy nuts) until a "click" sound is heard—indicating the cylinder has completed plastic deformation and tightly engaged with the hole wall;
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Inspect the effect: After installation, use a caliper to measure the flatness of the head, ensuring it is flush with the surface of the connected component. Use a torque wrench to test the torque for screwing in the matching bolt; for example, an M5 specification 304 stainless steel rivet nut should have a screwing torque of 8-10N・m, with no thread slipping or loosening considered qualified.
(3) Special Scenario Handling
If the connected component is a composite material (e.g., aluminum-plastic panel, carbon fiber panel), a metal bushing must be pasted on the inner wall of the prefabricated hole to enhance hole wall strength and prevent material cracking during riveting. For curved surfaces, a custom flat head with a radian is required to ensure full contact with the surface; if necessary, place a thin gasket between the head and the connected component to prevent excessive local stress.
IV. Maintenance and Troubleshooting: Extend Service Life and Avoid Failure
(1) Daily Maintenance Key Points
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Regular inspection: Inspect every 6 months for ordinary scenarios, and every 3 months for humid or vibrating scenarios. Focus on checking whether the head protrudes and whether the thread is rusted; gently twist the bolt with a wrench to confirm no loosening;
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Rust prevention: For galvanized steel with slight rust, sand it with fine sandpaper and apply anti-rust paint; for 304 stainless steel contaminated with acid-alkaline substances, rinse immediately with clean water and dry to avoid thread corrosion;
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Standardized disassembly: Prioritize using a hexagon socket wrench for disassembly. If the bolt seizes with the nut, drop a small amount of lubricating oil on the thread, let it stand for 5 minutes, then rotate slowly (forced twisting to avoid thread damage is prohibited).
(2) Common Troubleshooting
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Loosening after riveting: Mostly caused by an excessively large prefabricated hole or insufficient pressure. Re-machine a prefabricated hole that meets specifications and re-rivet at standard pressure;
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Head protrusion: Caused by an excessively long cylinder or excessive pressure. Replace with a nut with a shorter cylinder and reduce the riveting pressure to the standard range;
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Thread slipping: If it occurs at the drive end, simply replace the wrench; if internal thread slipping occurs, replace with a new nut (continued use is prohibited to avoid component damage from bolt falling off).
V. Conclusion: Scientific Use to Maximize Value
The use of flat-head internal-external hexagon blind-hole rivet nuts should follow the logic of "first understand, then select, then install, and regularly maintain." Start from structural characteristics to match application scenarios, ensure parameter adaptation through precise selection, control details with standardized installation steps, and extend service life through regular maintenance.
Whether for precision connections in electronic equipment or safe fixing in medical devices, only by mastering correct usage methods can the advantages of "dual drive," "blind-hole adaptation," and "surface flushness" be fully utilized—ensuring reliable connections and avoiding equipment failures or safety hazards caused by improper operation.
