This is fastener standard for bolts:
Grade 8.8 means, Approx. 800 Mpa tensile strength and 640 MPa yield strength (you will arrive at the YS by multiplying both the numbers times 10. That is 8x8x10=640)
Similarly, 10.9 means approx.1000Mpa TS and 900 Mpa yield strength. See the below-given details.
The grade 8.8 refers to the tensile strength which is generally 116,000 psi, grade 10.9 is generally 150,000 and grade 12.9 is generally 175,000 psi. Grade 8.8 high tensile steel is often referred to as the structural grade for bolts.
| Material | Property Class | Tensile Strength, Mpa | Hardness | Heat Treatment | Tempering |
|---|---|---|---|---|---|
| Low or medium carbon steel with max limits for C 0.55, P0.048, S0.058 | 4.6 | 400 | B67-B87 | No | |
| Low or medium carbon steel with max limits for C 0.55, P0.048, S0.058 | 4.8 | 420 | B71-B87 | No | |
| Low or medium carbon steel with max limits for C 0.55, P0.048, S0.058 | 5.8 | 520 | B82-B95 | No | |
| Medium carbon steel with max limits for C0.28- 0.55, P0.048, S0.058 | 8.8 | 830 | C23-C34 | Oil Quenched | min 425°C |
| Medium carbon steel with max limits for C0.28- 0.55, P0.048, S0.058 | 9.8 | 900 | C27-C36 | Oil Quenched | min 410°C |
| Medium carbon steel with max limits for C0.28- 0.55, P0.048, S0.058 | 10.9 | 1040 | C33-C39 | Oil Quenched | min425°C |
| Medium carbon steel with max limits for C0.31- 0.65, P 0.045 MAX, S 0.045MAX | 12.9 | 1220 | C38-C44 | Oil Quenched | min 380°C |