It depends on the application scenario. In interference-fit holes, tighten the nut. When the bolt head and nut have different shapes/diameters, apply torque to the side with the smaller bearing surface (if the bolt head is smaller than the nut, tighten the bolt head). When clamping dissimilar materials, tighten on the side with the lower coefficient of friction. For long bolts, tighten the nut to avoid twisting and winding.

Use a torque tool or hand wrench to calculate the torque using the formula T=KFD (K is the nut factor, which needs to be calibrated according to the actual situation). Consider the effects of friction between threads and on the contact surface. It is recommended to use digital twin technology to monitor the preload force in real time to avoid overloading or underloading.

Strictly control the cleanliness of the friction surface. Flame cutting and hammering are prohibited. Use a calibrated torque wrench to ensure that only 2-3 threads are exposed. Shear bolts should have their heads cut off. Large hexagonal bolts should be marked with the initial/final tightening procedures and sealed with paint.

Regularly spot-check and tighten bolts, and replace loose, rusted, or damaged parts. Use specialized tools to ensure preload, and integrate digital twin models to predict environmental impacts (such as wind loads and temperature fluctuations) to adjust maintenance plans in advance.

By mapping real-time data to a virtual model, equipment health can be monitored and fatigue or corrosion risks can be predicted. For example, a photovoltaic rack system can use digital twins to analyze stress changes during sandstorms or high temperatures, optimizing maintenance cycles and reducing O&M costs.