Tensile Strength of a Grade 8 Bolt
| Value | 1,034,000,000 Pa |
| Status | Conventional / typical value |
| Source | SAE J429 / Machinery's Handbook, 31st ed. |
| Categories | Material PropertiesEngineering & Trademechanics |
| pascal | 1,034,000,000 Pa |
| kilopascal | 1,034,000 kPa |
| megapascal | 1,034 MPa |
| bar | 10,340 bar |
| atmosphere | 10,204.787 atm |
| millimeter of mercury | 7,755,636.7 mmHg |
| pound per square inch | 149,969.02 psi |
| foot of water column | 345,927.35 ft H₂O |
| gigapascal | 1.034 GPa |
| kip per square inch | 149.96902 ksi |
| inch of mercury | 305,340.03 inHg |
| inch of water column | 4,151,128.2 in w.g. |
Learning zone
Grade 8 (six radial lines on the head, medium carbon alloy steel quenched and tempered) delivers 150 ksi minimum tensile, 130 ksi yield and 120 ksi proof — about 40 % more clamp capacity than Grade 5 for the same thread. Metric class 10.9 is the close equivalent. Higher preload is the actual product: a properly tensioned joint resists fatigue and loosening because the bolt sees only a fraction of the external load until the joint separates.
The trade-off is toughness and environment. Higher-strength steels are more notch-sensitive and far more susceptible to hydrogen embrittlement — which is why electroplated high-strength fasteners must be baked after plating, and why Grade 8 or A490 fasteners in aggressive or cathodically protected environments can fail hours or months after installation with no warning. Never substitute a Grade 8 into a joint designed around Grade 5 preload without rechecking the clamped members: the same torque now yields the flange instead of the bolt.