Galvanized hex Bolts andNuts Screw Fastener
What precautions should be taken when using hex bolts and nuts?
1. Torque control is crucial.
Tighten to the standard torque (see the table below). Overtorque can cause the
hex head bolts and nuts to break during tension, while undertorque can cause loosening.
Calibration tools: Electric torque wrench > Manual wrench > Adjustable wrench (do not use an adjustable wrench!).
| hex head bolts Grade |
M10 Recommended Torque (N·m) |
M20 Recommended Torque (N·m) |
| Grade 8.8 |
45-60 |
350-450 |
| Grade 10.9 |
70-90 |
550-700 |
| Grade 12.9 |
100-130 |
800-1000 |
2. Matching Principles
Material mixing is prohibited:
High-strength hex bolts must be paired with nuts of the same grade (e.g., g
rade 10.9 hex bolts with grade 10 hex nuts). Required Washers: Use hardened washers to distribute pressure and prevent deformation of the joint (thickness ≥ 1/10 of the bolt diameter).
3. Surface and Lubrication
Thread Cleaning: Remove swarf and oil stains before installation (otherwise, torque accuracy will be compromised).
Lubricant Selection:
Normal Environments: Apply molybdenum disulfide grease (reduces friction and provides more accurate torque).
High-Temperature Environments: Use copper-based or graphite lubricant (temperature resistance > 500°C).
