The use of a torque wrench is advisable wherever a joint requires tightening to a specified torque. If the torque wrench is correctly set, it trips when that torque is reached and displays the correct torque value. This is an important basic prerequisite to achieve the correct target torque. But that alone is sometimes not enough: another crucial aspect is adherence to the extension, which can vary from one torque wrench to the next. That is why it is necessary to deal with the topics of the point of force application and the extension. Even if the wrong extension is used, the torque wrench will trigger or display a value – but be aware that target values will not be correct!
The tightening torque corresponds to the applied force multiplied by the length of the lever arm. The point of application of force defines the point on the lever arm at which the user's hand actually applies force to the tool. This is important to know for these reasons:
The right choice of torque wrench can significantly minimise this risk.
Another common source of errors are insert tools. If they have a different extension (S) from the standard extension (SF) for that torque wrench, this will also falsify the measurement result. The display or setting value (W) of the torque wrench will then have to be corrected. In other words: users have to recalculate the torque they want to set. If you skip this important step, the fastener will be tightened with the wrong torque!
The corrected display or setting value (WK) is calculated using these formulas:
You can find more information and sample calculations in our STAHLWILLE product catalogue