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How Does a Torque Wrench Work (Our Secret)

In the struggle to reduce the car’s weight, in modern models, many parts are maximally lightened, and even threaded connections today are designed for a certain effort without having a safety margin.

Therefore, it is essential during repairs to use the wrenches with a tightening torque.

When using conventional wrenches, tightening the threaded connection is possible.

As a result, the thread may be torn off, and the two connecting surfaces that are not designed for increased load are also partly damaged due to exceeding the maximum permissible tightening torque.

Consider the design and operation of this type of tool.

How Does a Torque Wrench Work

Design features and application

The following elements are provided in the construction of a torque wrench:

  • two-armed levers;
  • lock nut;
  • grooved handle;
  • spring.

Even though the parts are pretty simple, the torque wrench serves a critical task. It has become widespread in the construction of engineering communications and the field of car maintenance.

Today manufacturers offer several types of this tool. Accordingly, the principle of their operation is different, and therefore, before use, you should study the attached instructions in detail.

Let us briefly consider the principle of operation of each type of torque wrench.

Types of Torque Wrenches

Depending on the device and the principle of operation, there are three types of torque wrenches: torsion (arrow), spring-loaded (ratchet), and digital (electronic).

Torsion Calibration Wrench

The device works on the principle of a dynamometer. The simplest dial key is a knob with a spring steel lever, on which an arrow is fixed. A scale is fixed on the handle, according to which the moment of force is determined.

Torsion Calibration Wrench

When the handle is loaded, the lever bends, and the position of the pointer shifts along the scale. This allows you to determine the tightening torque.

There is a type of torque wrench with a built-in digital type indicator.

This makes the tool easier to use and prevents accidental damage to the indicator arm.

The advantages of the arrow key are low cost and the presence of a double-sided scale to control the tightening of the left and right threads.

 Disadvantages of torsion wrenches:

  • Low accuracy,
  • Which deteriorates with wear;
  • The complexity of use in hard-to-reach places;
  • Lack of a ratchet mechanism.

At the heart of such a tool is a ratchet. This mechanism is located in the key’s handle and is triggered when the required tightening torque is reached.

To use the wrench, you must independently set the necessary tightening torque and tighten the nut until it clicks, indicating that the mechanism has triggered.

The ratchet mechanism will not allow further tightening of the nut since the key will scroll. The only drawback of such a tool is the need to adjust the tightening torque every time.

Therefore, manufacturers also offer non-adjustable torque wrenches. The manufacturer sets them at a specific tightening torque.

Spring-loaded torque wrench

They are convenient because they do not require adjustment but are less functional since they are designed for only one moment.

Electronic torque wrench

Unlike spring-type torque wrenches, electronic ones are more functional.

They have a digital display to show the current tightening torque and select the unit of measure for this parameter.

Electronic keys have the lowest percentage of error – no more than 1%. They must be used in the following sequence:

  • The required tightening value is set on the key;
  • The head is put on per the size of the nut;
  • The nut is tightened to the required torque, which is displayed on the electronic display.

What Are Torque Wrenches for?

Many of us use ordinary locksmith wrenches to tighten all the joints encountered in the process. However, this is wrong – in plumbing work, it is often required to observe a particular tightening force strictly. Consider the possible consequences:

The bolt is too loose:

  • Loose connection of the nodes;
  • It is possible to untwist the connection during operation.

The bolt is tightened too tight:

  • Destruction of the bolt due to overcoming the yield point (the threshold at which a loaded bolt can regain its shape after removing the load);
  • Thread breakdown;
  • Broken or ineffective spring washers (spring washers).

To avoid these consequences, the manufacturer indicates the required tightening force for critical connections – to comply with it, we need a torque wrench.

Tips For Using Torque Wrenches

How Does a Torque Wrench Work

  • To maintain the maximum accuracy of operation, the key must be in the room where the work will be performed for at least three hours – this will allow the spring of the mechanism inside the key to adapt to the temperature;
  • Avoid the use of adapters between the landing square of the key and the socket head – this can lead to an increase in the operation error of the mechanism;
  • After work, set a zero value to unload the spring (otherwise, the mechanism will be subjected to a long-term static load, which will affect the measurement accuracy);
  • Do not use a torque wrench as a tool to tear off screw fasteners.
  • Check the instrument regularly to maintain accuracy.

What to Look For when buying a Torque Wrench

The best choice for an auto torque tool is a set of several wrenches of different designs. First, you need to understand the dynamic range in which puffs are made in your car.

It is not difficult to do this, and you need to take the technical description and see the maximum and minimum digital values. Within these limits, select the tool.

A special question: “how do you check these keys at home?” With digital products, everything is clear, the previous values ​​zero out, and that’s it.

The situation is more complicated with limit, scale, and arrow keys. It is not easy to arrange a normal calibration stand at home or in the garage.

Therefore, you will have to take the instrument to the laboratory periodically.

Before purchasing precision wrenches, it is a good idea to know their key performance characteristics. Here they are:

  • Maximum gain. A value beyond which no force can be applied to a particular instrument, the boundary of a scale mark, digital range, or engraving.
  • Moment of power. Mathematically, it is the product of the force by the radius vector, while the force is also a vector quantity. Expressed numerically in units of Newton per meter or Nm. The main calculated value is she who is indicated in the instructions.
  • The size of the square. This value determines which nozzles and heads are suitable for a particular wrench.
  • Torque range. It is determined by the limits of the maximum and minimum efforts at which a specific vital works; it is simpler – these are the boundaries of the scale. It is not recommended to buy a tool if it operates near peak values ​​- this reduces accuracy and increases the likelihood of device failure.
  • Accuracy. Digital keys have the highest accuracy, dial, arrow, and limit keys have slightly worse performance.
  • The weight. This is not such a significant value; every motorist is quite capable of working with any torque wrenches.
  • Length. Here you need to take into account the layout and arrangement of the units of each vehicle so that a situation does not happen when the size of the tool does not allow them to operate in a confined space.
  • Ratchet. A convenient, functional device that greatly facilitates work.


Thus, regardless of the type of torque wrench, professionals and novice artisans can work with it. A mechanical torque wrench can handle most car repair tasks.

When installing small fastening screw connections that do not require a high tightening torque, it is recommended to use more accurate electronic counterparts.

There are some other interesting devices that do a ton of things that torque wrenches do. Check out how do torque sticks work to read a little more about this.

Stewart Kaplan
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