08.09.2026
Modified extension length: cause of incorrect bolted connections
Inhalt
Interchangeable insert tools make the torque wrench a more versatile tool. For example, a ratchet can quickly be changed for an open jaw or ring insert tool. And then a modified extension length needs to be taken into account – with mechanical torque tools, this requires a manual calculation and with electronic tools, it is often done automatically. But if you forget to correct the extension length or make a mistake in your calculation, the bolted joint will be wrong. This article will explain why this is the case and why eClick from STAHLWILLE is the solution.
Insert tools can come in various lengths and change the length of the force loading point. But, take note: the force loading point, i.e. the distance between the force application point and the bolt, is one of the variables used to calculate the torque because torque is the force applied (measured in Newtons) multiplied by the length of the force loading point (measured in metres).
01.
Torque is dependent on the force loading point
This means that as the force loading point is extended, less force is needed to attain the tightening torque. If the force loading point is shortened, more force has to be applied to tighten the bolt to the required torque. Depending on the insert tool used, you will therefore have to recalculate the specified tightening torque before setting it on the torque wrench.
02.
Extension length: how to recalculate
But how do you know how to recalculate the tightening torque? This is precisely where the extension length comes in. It tells you the length of the distance between the centre of an insert tool's square drive and a fixed reference point on the torque wrench – and consequentially, the deviation from the torque wrench's standard extension length (SF). The corrected tightening torque (WK) can then be calculated using this formula:
03.
Greater reliability, fewer calculations: eClick
There are therefore two potential sources of mistakes: you may simply forget to correct the extension length or you may make a mistake in calculating the correction. In either case, the traditional recalculation method takes time. And this is why STAHLWILLE has added a special function to its eClick torque wrench – the wrench which measures digitally and clicks mechanically: you simply enter the modified extension length in the settings and the tool does the rest. Benefit from tangibly higher levels of reliability and efficiency!
04.
Frequently asked questions about extension length when using torque wrenches
Put simply: when you use an insert tool, the length of the force loading point may be extended or shortened. Since the force loading point affects the torque acting on the bolt, the applicable tightening torque has to be adjusted.
Company
Service
2026© All Rights Reserved