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How Does an Impact Wrench Work? – All Types Explained

How Does an Impact Wrench Work
Written by Brent Butterworth
Last Update: May 3, 2023

Torque wrenches were born as a necessity. These tools powered the automotive industry like never before, improving the performance of workers on an assembly line. However, the high demand for cars and other products demanded the invention of a more powerful and faster tool.

The solution to the problem came with the invention of the first impact wrench. These tools let you apply high torque without effort. While in the past workers had to use muscular force to tightening or loosening bolts, now they only needed to pull a trigger to get the job done.

If you’re curious to learn more about these wonderful tools, you’re certainly in the right place. Today we’ll explain you how does an impact wrench work and we’ll show you all the different types currently available on the market. Finding the best impact wrench for you will be much easier once you go through this guide.

Impact Wrench Types

  • Electric

Electric impact wrenches are powered by electricity. They can be corded or cordless. Corded models need to be plugged into an outlet to work. They’re very powerful but not practical when you need to use them in places away from electric power sources.

On the other hand, cordless models use a brushless motor powered by a nickel-cadmium or lithium battery. Brushless motors have a superior lifespan because they don’t produce friction between the rotor and the stator. This means less waste, less noise, and less maintenance.

However, brushless motors aren’t as powerful as conventional electric motors. So, the torque generated by a cordless impact wrench is quite limited compared to a corded impact wrench. Also, batteries tend to discharge too quickly, forcing you to stop during work to recharge.

Cordless models are a lighter and more portable option compared to corded impact wrenches. Also, they’re perfect to work on difficult corners where working with an electric cord is uncomfortable.

  • Pneumatic

Pneumatic impact wrenches are powered by compressed air. So, they necessarily need to be connected to an air compressor to work. Pneumatic models are much more powerful than the electric types when compared, but they’re much more difficult to transport.

So, if you intend to carry your pneumatic tool to different places, make sure the air compressor has big and resistant wheels.

Unlike electric models, pneumatic impact wrenches don’t let you to adjust torque. So, it isn’t recommended to use them on rusted bolts, because excessive torque may break them.

  • Hydraulic

Hydraulic impact wrenches are the most powerful of all. They’re stationary and are usually used for industrial purposes. These tools are powered by hydraulic fluid pumped at high pressure.

Understanding How Does An Impact Wrench Work

Parts of an impact wrench

Impact wrenches use a motor and a spring to accelerate a rotating mass known as a hammer (no, we are not talking about the framing hammer). During this process, the hammer hits the output shaft (also known as anvil) to generate torque impact.

In a single revolution, the hammer hits once or twice the anvil. Those models that deliver only one hit per revolution can generate more torque than the rest.

Usually, the hammer is able to rotate and slide on a pivot while a spring holds it at the bottom. There’s also a steel ball between the anvil and the hammer. This steel ball slides the hammer backwards and compresses the spring at the bottom if the input shaft spins ahead of the hammer.

Below the hammer there are metal teeth that lock the hammer, turning the acceleration into torque impact. When the hammer stops, the input shaft keeps turning and slides the steel ball forward. At this point, the hammer and spring are released to restart the cycle.

When there’s no high load on the rotating head of the wrench, the ball won’t compress the spring and the impact wrench will run smoothly as a common drill.

On other models, there are two pins on the input shaft that work as clutches. In this configuration, the metal ball compresses the pins against a spring. When the pins slide outwards, they hit the anvil and generate torque impact. In this case the hammer speeds up much more and applies more torque. However, the higher impacts also tend to damage the teeth.

Another configuration uses a swinging weight and a protrusion around the anvil’s pivot. While the hammer rotates, the swinging weight is placed in position for impact after hitting the anvil. Finally, the swinging weight transfers the energy of the impact to the rotating head of the wrench.

This configuration delivers a single hit per revolution, which means a greater torque generation. However, it also transfers too much vibration, which is annoying for some users.


As you can see, not all impact wrenches work the same way. There are at least three different ways to generate torque for safely tightening and loosening bolts. However, in each case, the principle is always the same. A rotating hammer that hits an anvil and transfers the energy of the impact to the spinning head of the wrench.

Now that you know how does an impact wrench work, you can quickly identify each of its parts and the possible causes of a certain failure. Indeed, the more you know your tool, the better prepared you’ll be to properly use it.


Q. 1: Is it possible to use an impact wrench as a drill?

Yes. You can adapt a drill bit to your impact wench to use it as a drill. However, in these cases it’s recommended to use a model with a torque adjustment system.

Q. 2: Can you use an impact driver as an impact wrench?

Yes. An impact wrench can perform all the basic functions of an impact driver. However, impact wrenches are much more powerful than impact drivers.

Q. 3: What is the best compressor for an impact wrench?

It all depends on the air pressure and the CFM required by your wrench. You can find these requirements on the user manual of the product.

Q. 4: Is it possible to use an impact wrench to loosen lug nuts?

Yes. You can use a torque wrench for loosening and tightening lug nuts. If you intend to use an air impact wrench, you should be careful to not exceed the applied torque so as not to break the nuts.

Q. 5: What is the main purpose of impact wrenches?

Impact wrenches were initially created for tightening and loosening bolts without the application of muscular force. However, modern models can also work as drills and impact drivers.

Q. 6: When it isn’t recommended to use an impact wrench?

It isn’t recommended to use an impact wrench when the minimum torque generated by the tool exceeds by far the torque required by the bolts. It’s also not recommended to use them when the bolts are rusted or visibly damaged.

About the author

Brent Butterworth

A Professional Woodworker & Custom Furniture Builder

Brent lives in Wisconsin and is a woodworker, custom cabinetmaker, interior consultant, and a freelance writer who got the opportunity to write several magazine articles for different publications on home improvement and woodworking. He’s always amazed at the depth and breadth of woodworking all over the globe, and feels proud to be a part of this great effort. Brent has built everything one can imagine, from unique art furniture to different types of home furniture to canoes and even a sailboat.

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