Introduction to GB/T 3098.5-2016 Standard
The GB/T 3098.5-2016 standard specifies the mechanical properties of self-tapping screws, which are essential fasteners designed to form their own threads in materials such as metals, plastics, and wood without the need for pre-drilled holes. This standard ensures reliability in applications ranging from automotive assembly to construction and electronics manufacturing.
As a critical reference for engineers and manufacturers, it outlines requirements for surface hardness, case hardening depth, core hardness, and performance in tapping tests. Adhering to these specifications guarantees that screws can withstand specified loads without failure, promoting safety and durability in end products.
- Defines minimum and maximum values for key mechanical attributes to ensure consistent quality.
- Applies to carbon steel self-tapping screws with various thread sizes from ST2.2 to ST9.5.
- Incorporates testing protocols for tapping performance and torsional strength.
This standard is part of the broader GB/T 3098 series on fastener mechanical properties, aligning with international norms like ISO 2702 for global compatibility.
Mechanical Property Requirements
The standard details precise mechanical properties for self-tapping screws across different thread designations. These include surface hardness measured in Vickers units (HV), case depth for carburized layers, core hardness ranges, standard test plate thicknesses and hole diameters for tapping performance, and minimum breaking torque values.
Surface hardness ensures the screw’s ability to penetrate and form threads effectively. Case depth controls the hardened layer’s thickness, balancing toughness and wear resistance. Core hardness provides internal strength to prevent brittle failure. Tapping tests simulate real-world installation, while breaking torque verifies torsional integrity.
| Property / Thread | ST2.2 | ST2.6 | ST2.9 | ST3.3 | ST3.5 | ST3.9 | ST4.2 | ST4.8 | ST5.5 | ST6.3 | ST8 | ST9.5 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Surface Hardness (min) | 450 HV 0.3 | 450 HV 0.3 | 450 HV 0.3 | 450 HV 0.3 | 450 HV 0.3 | 450 HV 0.3 | 450 HV 0.3 | 450 HV 0.3 | 450 HV 0.3 | 450 HV 0.3 | 450 HV 0.3 | 450 HV 0.3 |
| Case Depth (min) | 0.04 | 0.04 | 0.05 | 0.05 | 0.05 | 0.1 | 0.1 | 0.1 | 0.1 | 0.15 | 0.15 | 0.15 |
| Case Depth (max) | 0.1 | 0.1 | 0.18 | 0.18 | 0.18 | 0.23 | 0.23 | 0.23 | 0.23 | 0.28 | 0.28 | 0.28 |
| Core Hardness (range) | 270 HV 5 to 370 HV 5 | 270 HV 5 to 370 HV 5 | 270 HV 5 to 370 HV 5 | 270 HV 5 to 370 HV 5 | 270 HV 5 to 370 HV 5 | 270 HV 5 to 370 HV 5 | 270 HV 10 to 370 HV 10 | 270 HV 10 to 370 HV 10 | 270 HV 10 to 370 HV 10 | 270 HV 10 to 370 HV 10 | 270 HV 10 to 370 HV 10 | 270 HV 10 to 370 HV 10 |
| Test Plate Thickness (min) | 1.17 | 1.17 | 1.17 | 1.17 | 1.85 | 1.85 | 1.85 | 3.1 | 3.1 | 4.67 | 4.67 | 4.67 |
| Test Plate Thickness (max) | 1.3 | 1.3 | 1.3 | 1.3 | 2.06 | 2.06 | 2.06 | 3.23 | 3.23 | 5.05 | 5.05 | 5.05 |
| Test Plate Hole Diameter (min) | 1.905 | 2.185 | 2.415 | 2.68 | 2.92 | 3.24 | 3.43 | 4.015 | 4.735 | 5.475 | 6.885 | 8.27 |
| Test Plate Hole Diameter (max) | 1.955 | 2.235 | 2.465 | 2.73 | 2.97 | 3.29 | 3.48 | 4.065 | 4.785 | 5.525 | 6.935 | 8.33 |
| Breaking Torque (min, N·m) | 0.45 | 0.9 | 1.5 | 2 | 2.7 | 3.4 | 4.4 | 6.3 | 10 | 13.6 | 30.5 | 68 |
Note: All dimensions are in millimeters unless specified otherwise. Hardness values are tested under specified loads (e.g., HV 0.3 indicates Vickers hardness with 0.3 kgf load).
- Ensure screws are heat-treated to achieve the required hardness levels for optimal performance.
- Use calibrated equipment for hardness and torque testing to comply with the standard.
- Consider material compatibility when selecting screw sizes for specific applications.
Alternative Standards
For international equivalence, refer to ISO 2702-2011, which provides similar specifications for heat-treated carbon steel tapping screws. This standard can be used interchangeably in many global contexts, ensuring cross-compatibility in design and procurement.
Download ISO 2702-2011 PDF
よくある質問（FAQ）
- What is the significance of surface hardness in self-tapping screws?
- Surface hardness, set at a minimum of 450 HV 0.3, ensures the screw can effectively cut and form threads in the target material without deforming or wearing prematurely, critical for reliable fastening in high-stress environments.
- How is case depth measured and why is it important?
- Case depth is measured via metallographic examination after carburizing. It ranges from 0.04 mm minimum for smaller screws to 0.15 mm for larger ones, providing a hard outer layer while maintaining a tougher core to resist cracking under load.
- What does the breaking torque test indicate?
- The breaking torque test, with minimum values from 0.45 N·m for ST2.2 to 68 N·m for ST9.5, verifies the screw’s torsional strength, ensuring it can be installed without fracturing and withstand operational torques.
- Are there specific testing conditions for tapping performance?
- Yes, tests use standard plates with defined thicknesses (e.g., 1.17-1.3 mm for ST2.2) and hole diameters (e.g., 1.905-1.955 mm). These simulate installation scenarios, confirming the screw’s ability to tap without stripping or failing.
- How does GB/T 3098.5-2016 compare to ISO 2702?
- Both standards are aligned in mechanical property requirements, but GB/T 3098.5-2016 is tailored for Chinese manufacturing, while ISO 2702 offers broader international acceptance. Always verify equivalency for specific projects.
- What materials are typically used for screws under this standard?
- Primarily carburized carbon steel, heat-treated to meet hardness specs. Stainless steel variants may require separate standards, as this focuses on carbon steel for general industrial use.
