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How to Use an Impact Wrench

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Old, rusty bolts and over-tightened automotive parts can be extremely difficult, and in some cases, impossible to remove with a hand wrench. On the other side of the coin, some fasteners where only a small pilot hole is used can be very hard to screw into hard wood.

In these cases where you need a little (or a lot) more power, knowing how to use an impact wrench will come in very handy.

Different Kinds of Impact Wrenches

Impact wrenches generally fall into two different categories, pneumatic (air) or electrically powered. Air wrenches are commonly seen quickly taking the nuts off tires and in other mechanical or industrial settings.

Electric impact wrenches are normally more portable, and their (generally) smaller size allows for more use around the house.

Impact wrench being used to remove nuts off a tire

Pneumatic Impact Wrenches

Using forced compressed air to generate power by flowing quickly over vanes inside the impact wrench body, pneumatic impact wrenches are able to generate a tremendous amount of torque. They do need to be attached to an air compressor, but this also adds an additional layer of control over how much force is generated.

In addition to the adjustment settings that normally come in the form of a dial on air impact wrenches, it is also possible to reduce or increase the amount of pressure that the compressed air is under in the air compressor. This is measured in Pressure per Square Inch (PSI). Check the manufacturer’s instructions for the recommended PSI to use with your impact wrench.

Electric Impact Wrenches

As the name suggests, electric impact wrenches use electricity to generate the spinning motion that powers the hammer motion. While not able to reach the sheer force that air wrenches can generate, they do a good job for almost everything other than heavy mechanical work.

They are separated into two categories, corded and cordless.

Corded electric impact wrenches plug into a standard wall socket or gas-powered generator. Since the cord may be a limiting factor on how far you can travel with the wrench, be sure to measure the distance and use a correctly rated extension cord if needed.

The best corded impact wrench for the money can generally produce more torque than cordless wrenches, and you do not have to worry about the battery running out.

Cordless electric impact wrenches are powered by rechargeable batteries, normally inserted into the handle. Every year the amount of power the batteries can store and the running time increase with better technology, but the fact is that the batteries will run down over time.

In addition, they will begin to lose their maximum charge as they age.

Which Impact Wrench to Use

  • Air impact wrenches may be necessary for bigger jobs, but consider the added expense of the air compressor.
  • Corded electric impact wrenches are a fair compromise between power and portability.
  • Cordless electric impact wrenches will have less power, but can be used in any environment. For most home jobs, a cordless impact wrench would be our recommendation.
An impact wrench lying on a table beside a pile of screws

Preparing to Use an Impact Wrench

Some preparations need to be made before using any power tool, or for that matter, starting any project. The recommendations below are a mix of common sense and impact wrench specific topics.

  • Prep the working area – Make sure an air compressor or electric outlet is available, depending on the type of impact wrench being used.
  • Check battery – Avoid using depleted batteries. They will run out quickly and reduce the lifespan of the batteries.
  • Make sure you have the right type of socket – Only use sockets identified as being compatible with an impact wrench. Home socket wrench sets will not have strong enough sockets for use with this tool.
  • Make sure you have the right size socket – An incorrectly sized socket, even one that is only a millimeter too large, can (and probably will) damage the socket, the bolt, the impact wrench, you, or possibly all of the above. 
  • Attach the socket – Follow the manufacturer’s instructions on how to attach a socket bit to the impact wrench shaft.
  • Put on safety equipment – Eye protection is necessary when using an impact wrench. Ear protection is recommended, especially when connected to an air compressor – they can get very loud.
  • Assemble the wrench – Attach the air hose if using a pneumatic wrench. Check for any kinks in the hose. Attach the battery if using a cordless electric impact wrench.
  • Set the wrench direction – Make sure the direction is correctly set for inserting or extracting your bolt.
  • Test to make sure it spins – A simple test, but be sure that power is getting to the wrench shaft, and the shaft is spinning in the right direction.
  • Set impact wrench speed – There should be an adjustment dial on the impact wrench to adjust the speed for your application. For more fine-tuning, you can also adjust the PSI coming from the air compressor when using an air wrench.

Learn the differences between an impact driver vs wrench!

Using an Impact Wrench for Attaching

  1. Place the bolt or nut it in the correct place to be attached, and begin threading it by hand. If the first thread is difficult to get past, check that it is not cross-threaded. 
  2. Continue turning the nut or bolt for at least a few threads, using a hand wrench if necessary. This ensures that it is connected securely and the threads are not misaligned.
  3. Check all the settings on your impact wrench – speed and direction being the most important.
  4. Place the socket at the end of the wrench over and around the nut or bolt being attached. Lightly turn the wrench back and forth to verify the socket fits correctly.
  5. Place two hands on the impact wrench for stability.
  6. Make quick, short pulls on the trigger of the impact wrench. This will help build up the turque that is needed. 
  7. Holding the trigger down constantly will still work, but quick bursts will help increase the hammering force that the impact wrench is known for.
  8. Be careful when getting to the end of the bolt and do not over tighten. Over tightening is very easy with an impact wrench! If possible with the application, consider reducing the wrench torque near the end.
  9. Remove the impact wrench and move on to the next attachment.
A close up of an impact wrench

Using an Impact Wrench for Removing

  1. Double check that it is too difficult to remove the nut or bolt with a hand wrench or standard drill with a socket attachment. An impact wrench is not always necessary.
  2. Consider dripping some lubrication such as tapping fluid in the threads if you can reach them.
  3. Verify the impact wrench settings. For removal of a large stubborn or frozen nut, you will want to use a high power setting. Be sure the direction is set to “reverse.”
  4. Align the socket with the bolt head.
  5. Hold the impact wrench with two hands.
  6. Depress the trigger using short bursts.
  7. If the nut does not immediately loosen, keep trying until it does.
  8. Increase the power if necessary.
  9. Once the nut or bolt is loosened, use steady pressure instead of bursts to remove it the rest of the way.
  10. Consider removing the last few threads by hand so the nut does not fall on the ground and roll away.

Conclusion

It is not difficult to use an impact wrench, but its power is hard to overstate, so be sure that the project actually requires one in the first place. Consider the space you will be working in and the projects to be handled before deciding on which type of impact wrench is right for you, and take care to follow instructions on how to use impact wrenches in a safe environment.