14.09.2026
Permanent pretensioning: impacts on accuracy of measurement
Inhalt
Most mechanically clicking torque wrenches and torque screwdrivers have an internal compression spring. These produce the resistance that has to be overcome when the target torque is reached – the torque tool clicks. You will learn here how this works and why the spring should be released if it is not used for long periods!
The compression spring inside the torque wrench or torque screwdriver holds the clicking mechanism in its starting position until the torque applied to the bolted connection exceeds the spring pretensioning. Then it releases the mechanism and the tool audibly and physically clicks. The higher the torque setting is (usually adjusted using a rotary knob or sliding scale), the more the spring is pretensioned, creating a greater resistance.
01.
Why the spring has to be released
If the torque tool is stored or not used for long periods, it is essential that the spring is released. This is because if it is permanently tensioned, the spring characteristics may change temporarily and the pretensioning force may fall. Then it doesn't stretch and relax like a rubber band. Temporary changes in the material structure may also result from the constant mechanical load.
02.
What happens if the spring isn't released?
There may be significant consequences. Because users can't see the loss in pretensioning force, they set the tightening torque as normal. So while the mechanism ‘clicks’ like normal, the click no longer occurs at the set torque and the bolted connection is incorrectly tightened. In a worst-case scenario, this puts people at risk and results in consequential damage.
03.
It's simple: release the spring!
After work, and certainly if the tool isn't going to be used for a long time, you should reset the torque tool to the lowest value on the scale. This releases the spring and does not subject it to additional pretensioning. This is the only way of ensuring that its pretensioning force and therefore the precision of measurements and clicks is retained for many years to come.
04.
It's even easier with eClick
eClick technology from STAHLWILLE is even more convenient. These torque tools, which measure electronically and click mechanically, do not have a traditional spring mechanism and there is no need to reset to ‘0’. Yet despite this you hear and feel eClick torque tools reach the target torque. They also allow you to set parameters digitally and download all bolting data. For greater process reliability, maximum transparency and comprehensive documentation.
This will take you to STAHLWILLE torque wrenches with eClick technology: eClick
The spring creates a defined pretensioning force, thereby allowing a torque to be set. The spring is responsible for ensuring that the wrench clicks when the set value is reached.
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