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Strength Grade Spec Table
Strength Grade KS Specifications — 9 sizes
ISO 898-1
This specification follows ISO (International Organization for Standardization) standards. ISO ensures cross-border compatibility, making it ideal for multinational projects, export equipment design, and global parts procurement.
ISO 898-1 bolt strength grade specifications. Lists tensile strength, yield strength, proof load stress, and hardness range for grades 4.6 through 12.9. The basis for bolt selection.
Practical Notes
- Grade marking: 8.8 → first digit (8)×100=800MPa tensile; second (0.8)×tensile=640MPa yield.
- Grades 10.9 and 12.9 are susceptible to hydrogen embrittlement. Always bake (hydrogen de-embrittlement) after pickling or electroplating.
ISOStrength Grade
9 sizes| Strength Grade | Tensile (MPa) | Yield (MPa) | Proof Load (MPa) | Hardness | Application |
|---|---|---|---|---|---|
| 4.6 | 400 | 240 | 225 | B71-B89 | General Bolt |
| 4.8 | 420 | 336 | 310 | B71-B89 | General Bolt |
| 5.8 | 520 | 416 | 380 | B82-B95 | General Bolt |
| 6.8 | 600 | 480 | 440 | B89-B95 | General Bolt |
| 8.8 | 800 | 640 | 580 | C22-C32 | High Strength (d≤16mm) |
| 8.8H | 830 | 660 | 600 | C22-C32 | High Strength (d>16mm) |
| 9.8 | 900 | 720 | 650 | C27-C36 | High Strength |
| 10.9 | 1040 | 940 | 830 | C33-C39 | UltraHigh Strength |
| 12.9 | 1220 | 1100 | 970 | C39-C44 | MaxHigh Strength (Black) |
FAQ
Where is bolt strength grade marked?
On hex bolt heads (top) and socket bolt heads (side). E.g., "8.8", "10.9", "12.9". No marking implies low grade (4.6–5.8).
Application difference between 8.8 and 10.9?
8.8 is standard for general machinery/structures. 10.9 is for automotive, aerospace, and high-load structures at 30–50% higher cost. 8.8 suffices for most mechanical fastening.