How does torque specification relate to fastener preload?

How does torque specification relate to fastener preload?

• A. The specified torque determines the temperature rating.
• B. The specified torque sets the length of the fastener.
• C. The specified torque corresponds to the desired preload (clamping force) in the fastener to achieve proper joint integrity.
• D. The specified torque is unrelated to preload.

Answer: (C)

Torque specification is the value used to reach a target preload in a fastener. When you tighten to that torque, the bolt stretches enough to generate the clamping force that holds the parts together. The specified torque is chosen based on fastener size, lubrication, material, and the required preload, because friction in threads and under the bolt head means the same torque won’t produce the same preload in every situation. This preload is what maintains joint integrity under service loads. If the torque is too low, the joint can loosen; if it’s too high, the bolt can yield or fail. Temperature rating and fastener length aren’t determined by torque in this way, and preload is indeed related to the torque applied under proper conditions.

Torque specification is the value used to reach a target preload in a fastener. When you tighten to that torque, the bolt stretches enough to generate the clamping force that holds the parts together. The specified torque is chosen based on fastener size, lubrication, material, and the required preload, because friction in threads and under the bolt head means the same torque won’t produce the same preload in every situation. This preload is what maintains joint integrity under service loads. If the torque is too low, the joint can loosen; if it’s too high, the bolt can yield or fail. Temperature rating and fastener length aren’t determined by torque in this way, and preload is indeed related to the torque applied under proper conditions.