* Bolt size (diameter and length): Larger diameter bolts require more torque. Longer bolts of the same diameter may also require slightly more due to increased friction.
* Material being fastened: The material's hardness and surface finish affect friction. Harder materials generally require higher torque.
* Lubrication: Using a lubricant (like anti-seize) significantly reduces friction, requiring *less* torque to achieve the same clamping force. Dry threads require *more* torque.
* Thread engagement: The amount of threaded portion engaged affects the clamping force. Shorter engagement requires less torque.
* Bolt pre-load: The target clamping force, which is what determines the necessary torque, needs to be calculated.
Therefore, you cannot find a universal torque specification for 8.8 grade bolts. You must consult a torque table specific to the bolt size, material being fastened, and lubrication used. These tables are often found in engineering handbooks, fastener manufacturer documentation, or online resources specific to the application.
To find the correct torque, you should:
1. Identify the exact bolt size (diameter and length).
2. Determine the material being fastened.
3. Specify the lubricant used (if any).
4. Consult an appropriate torque table or use a torque calculation method (which often involves considering the bolt's proof strength and the desired pre-load).
Using an incorrect torque can lead to either under-tightening (resulting in a loose joint and potential failure) or over-tightening (which can strip the threads, damage the bolt, or even cause the material to fail). If you're unsure, consult a qualified engineer or mechanic.
