Tightening torque, or torque value, is the force used to tighten a screw so that the joint remains securely fastened without overtightening or damage. The correct torque depends on the screw material, size, threads, lubrication, and the coating used (e.g. zinc flake coating).
Carbon steel screws are commonly used in structural joints. Their tightening torque is based on the material strength class (8.8, 10.9, 12.9) and standards such as ISO 898-1, and they can withstand high loads. Torque values vary; for example, for an M10 class 8.8 screw, the value is approximately 49 Nm (unlubricated).
Austenitic screws (e.g. A2-70 or A4-80) are corrosion-resistant, but they have lower yield strength than carbon steel. They require more precise torque control because they stretch more easily. For example, the recommended torque for an M10 A2-70 screw is approximately 35 Nm (unlubricated).
Always use torque tables provided by the manufacturer or standard, and take into account the effect of lubrication and coating – lubrication and coating can reduce the required torque by as much as 25–30%.