1. Appearance Inspection
Surface Treatment: High-quality screws have a uniform electroplating layer (such as colored zinc or white zinc), free of missing plating, blistering, or color variations. Low-quality screws often have burrs, pinholes, or shallow threads.
Head and Threads: The head should not be tilted or deformed, and the threads should be complete and without missing teeth. Thread accuracy can be verified using a go/no-go gauge test.
2. Dimensions and Tolerances
Key Parameters: Use a vernier caliper (accuracy 0.02mm) to measure the major diameter, minor diameter, and length of the thread. These must comply with standards (such as GB/T3098.5-2016).
Head Height: The head height of round-head screws should be measured using a dedicated caliper or projector to ensure consistency with the design.
3. Material and Hardness
Material Verification: Stainless steel screws (such as SUS304) can be distinguished using a chemical test. If the screw turns red, it is SUS201, and if it does not change color, it is SUS304. Carbon steel screws must be inspected for carburized layer thickness (0.05-0.1mm) and core hardness (270-370HV).
Surface Hardness: After heat treatment, the surface hardness of the screw must be ≥450HV. Untreated screws can be tested directly.
4. Performance Testing
Torque: For ST3.9 screws, the torque should be ≥1.3N·m. Avoid excessive fracture during testing.
Salt Spray Test: High-quality stainless steel screws must pass a 48-hour salt spray test to ensure no rust.
Hydrogen Embrittlement Risk: High-strength screws must be immersed in an acidic solution to simulate hydrogen penetration and test their ductility.
5. Functional Verification
Installation Test: Thread-cutting screws are tested in actual material (e.g., steel plate, plastic) to verify tight thread engagement and the absence of thread stripping or loose threads.
Security: Self-threading screws must pass a vibration test to ensure long-term stability. 6. Brand and Certification
Prioritize brands that have passed ISO9001 and CE certification (such as Jinyi and Dongming). For non-standard parts, a test report is required.
