Torque is the rotational force applied to tighten or loosen a bolt. It is commonly measured in units of force multiplied by distance (such as pound-feet or Newton-meters). Torque is used to achieve the desired tension or clamping force in a bolted joint.
When tightening a bolt, applying the correct torque is essential to ensure proper preload and to prevent under or over tightening. Under-tightening can result in inadequate clamping force, leading to joint failure or loosening, while over-tightening can lead to bolt or material damage, thread stripping, or joint distortion.
The specific torque value required for a bolt depends on factors such as bolt size, material, thread type, lubrication, and the application’s requirements. Manufacturers typically provide torque specifications in technical documentation or manuals specific to the bolt or the assembly being tightened.
It’s important to note that torque alone may not be sufficient for all bolted joints, especially in critical or specialized applications. Factors such as bolt type (e.g., torque-to-yield or controlled-angle tightening), joint design, and additional measures like pre-loading or tensioning may also be considered.
To ensure the proper torque is applied, it is recommended to use calibrated torque wrenches or other appropriate torque measurement tools. Following manufacturer’s guidelines and consulting with engineers or professionals experienced in bolted joint design and assembly is advisable to achieve the desired performance and safety.
ASTM A325 Bolt Torque Reference
| Bolt Size | TPI | Tension (lbs) | Torque (ft-lbs) |
|---|---|---|---|
| 1/2″ | 13 | 13,189 | 48 |
| 5/8″ | 11 | 22,577 | 109 |
| 3/4″ | 10 | 32,508 | 192 |
| 7/8″ | 9 | 44,332 | 314 |
| 1″ | 8 | 58,852 | 491 |
| 1-1/8″ | 7 | 75,180 | 678 |
| 1-1/4″ | 7 | 94,048 | 955 |
| 1-3/8″ | 6 | 114,880 | 1,239 |
| 1-1/2″ | 6 | 137,865 | 1,579 |
Please note that the torque values provided in the table are for illustrative purposes only and should not be considered as the definitive guide. It is crucial to refer to the engineering specifications, or professional recommendations for accurate and up-to-date torque requirements for ASTM A325 bolts in your specific application.