When bolts are installed by the direct-tension indicator, how is correct tension verified?

When bolts are installed using a direct-tension indicator (DTI), the verification of correct tension relies on the measurement of the gap between the direct-tension indicator and the bolt head. The DTI is designed to provide a visual indication of the tension that has been achieved during the installation.

As the bolt is tightened, the indicating mechanism in the DTI compresses and begins to create a gap. This gap is then measured to confirm that the tension has reached the specified level. It is critical that this measurement accurately reflects the tension in the bolt, as achieving the correct tension is essential for the structural performance and integrity of the assembly.

The other methods mentioned, such as listening for a sound or checking the weight, do not provide a reliable or standardized means of confirming bolt tension. Additionally, while a torque wrench is commonly used to achieve bolt tension, it does not directly indicate whether the desired tension has been reached, especially in cases where factors such as friction can affect the results. Therefore, measuring the gap between the direct tension indicator and the bolt head is the specific practice used to verify that the required tension has been attained.