Time：2025-08-12
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In modern industry, a reliable bolted connection and a trustworthy tightening tool are critical. Before production the tool must be calibrated and certified, and it must be re-checked during use to achieve optimum tightening quality and standards. Threaded-joint torque directly affects vehicle quality and operational reliability. Many factors influence the final torque: fastener material and diameter, thread surface roughness, friction coefficients between the bolt/nut and the contact faces, tool accuracy, tool speed, tightening sequence, and—crucially—the joint’s own characteristics.
Joint characteristics are classified as soft or hard based on their influence on torque build-up.
The joint uses soft materials or incorporates elastic elements (e.g., rubber gaskets).
After the mating surfaces touch, the fastener must be turned 324° or more to reach the target torque.
Torque decay can occur after tightening.
Example: head-lamp screws with rubber washers.
Joint members are stiff, rigid, and have smooth, well-mated contact faces.
After contact, ≤ 27° of additional rotation reaches the target torque.
Torque may “rebound” (over-tightening) after the driver stops.
Example: engine-block metal-to-metal joints.
ISO 5394:1994 defined soft as > 720° total rotation.
ISO 5393:2017 re-defined it: from 10 % to 100 % of target torque, the angle change must be ≥ 324°.
VDI/VDE 2647 uses 50 % → 100 % of target torque:
– Hard joint < 30°
– Soft joint < 360°
The apparent differences arise only from the reference angle used in each standard.
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