Impact wrenches are one of the most powerful handheld power tools and are widely used in the automotive industry to undo and tighten lug nuts of tires!

This article will provide you with all the relevant information on impact wrenches, their uses, types and how to use one!

Table of Contents

What is an Impact Wrench?

An impact wrench could be considered as a socket wrench on steroids and have been around a long time. They are power tools that are used for loosening or tightening of lug nuts, large bolts, and frozen or rusted fasteners.

Impact wrench - this one is sold by Ingersoll Rand
Ingersoll Rand Impact Wrench

To use a socket wrench the operator attaches a ratchet handle to the socket and by manually rotating the handle, the socket is driven in a clockwise or anti-clockwise direction to thread on or thread off something, be it a bolt into a nut, or a nut onto a threaded shaft… etc.

Occasionally it requires more torque (turning force) to loosen a bolt or a nut than the operator can provide using arm strength. A ratchet extension can be used sometimes to allow more torque to be applied manually, but sometimes the object to be loosened cannot be broken free manually.

Enter the impact wrench. The impact wrench takes most of the work out of turning the socket while the “impact” part of the impact wrench imparts greater force into rotating the socket than a person can and it can quickly break free stubborn bolts and nuts allowing them to be threaded off and on easily and with speed.

Impact wrenches provide a very high rotational torque which you cannot achieve with a regular power driver. They are able to achieve this by an internal hammering mechanism that transfers kinetic energy onto the output shaft.

How do Impact Wrenches Work?

So, what’s inside the basic impact wrench? How does the impact wrench work?

The basics are that and impact wrench is operated like any air tool. An air supply entering the impact wrench will force the rotational movement of vanes inside the tool, which will rotate the spindle, like an air drill, for example.

But then, a clever arrangement of springs, cams, an anvil and a hammer turn that rotational force into impact force, slamming into and turning the socket with speed and force.

Imagine you want to loosen a stubborn nut or a frozen bolt with a hand wrench. You may not be able to break loose the nut with the normal force from your hand. Maybe you could hit the wrench with a hammer? And after enough blows the nuts will effectively break loose. Well, in more simple terms, this is what happens inside an impact wrench.

Impact wrenches can be powered by an electric motor as well as compressed air, but air is the most popular so we’ll focus on that types working principle.

The air compressor will feed air into the tool which will drive the rotor and the rotor in turn will drive the hammer and hammer cage. During impact wrench operation, there is zero resistance on the output shaft (anvil), and so the driving motor power is transferred to the anvil.

What makes impact tools special? The hammer mechanism inside that actuates when the force is not sufficient. So, when the anvil faces resistance, the hammer slips from engaging the pin, causing it to rotate at a higher velocity and hence, a greater amount of energy is stored.

As it rotates, it is suddenly connected to the anvil, and this sudden impact of the rotating hammer transfers the stored kinetic energy inside the hammer to the anvil. Resulting in a very high twisting force on the output shaft (torque).

Once this sudden blow of energy is consumed, the output shaft may face the resistance again. If it does, the hammer slips and starts rotating and so the cycle repeats itself! These cycling blows are certainly what makes the impact wrench so powerful.

Here’s a look at how they work in a useful youtube demonstration!

Types of Impact Wrenches

The types of impact wrenches available are typically classified by their power source. Electricity and compressed air being the most commonly used sources of power for impact wrenches which leaves us with the 3 following types of guns:

  • Pneumatic Impact Wrench
  • Corded Impact Wrench
  • Cordless Impact Wrench

Let’s take a look at these in more detail!

Pneumatic Impact Wrench

The most widely used in automobile repair shops, automotive assembly lines and heavy equipment manufacturing is the compressed air powered impact wrench. They have some distinct advantages over the electric powered wrenches.

Air powered impact wrenches are relatively simple in their engineering design and so are inexpensive. The chances of malfunction is very rare as they have no electrical parts, with the biggest advantage being that they don’t get heated unlike its counterpart.

Any heat generated by the rotating elements inside the impact gun are cooled by the circulating compressed air. This makes the pneumatic impact wrench ideal for assembly lines where it can work for long hours continuously without the worry of overheating.

This overheat protection by the air flow and relatively simple design make the pneumatic impact gun more durable, and easy to repair and maintain.

On the downside, they need a continuous supply of compressed air. Small portable compressors found in the average DIY enthuasists garage may not be sufficient for these heavy jobs. Instead, a large air compressor unit able to provide the adequate supply of compressed air at a constant pressure would be needed.

It would be frustrating starting your work with a pneumatic impact gun and then having to wait for minutes before the compressed air reaches adequate pressure to let you continue. Visit our What Size Air Compressor Do I Need For Impact Wrench? article for more information!

These impact wrenches are available as 3/8″ 1/2″ 3/4″ and 1″ shanks. Here’s an example of a pneumatic Impact Wrench readily available on Amazon!

Advantages

  • Air cools rotating parts
  • Inexpensive
  • Longer life span

Disavantages

  • Limited control over speed and torque
  • Requires uninterupted supply of compressed air

Corded Impact Wrench

These electric impact wrenches that you need to plug into an electricity socker to power up have an electric motor fitted to the rear end of the tool that drives the hammer unit which transfers its motion to the output shaft.

Here’s an example of a corded impact wrench readily available on Amazon.

Advantages

  • Better speed and torque control
  • Easy to carry around since you don’t need an air compressor

Disadvantages

  • Expensive compared to air tools
  • Overheat due to moving parts

Cordless Impact Wrench

Another electric powered impact wrench, but this time by a battery. Cordless impact wrenches have one unique advantage over the other types in that they’re highly portable. You can throw them in your car trunk and use it anytime and anywhere you want to change tires.

The cordless design enables you to work in tight spaces, where a corded or air powered impact wrench wouldn’t be able to. However, the rechargeable batteries in a cordless impact wrench can get drained very quickly, especially if you use it continuously on stubborn nuts and bolts.

If selecting a cordless impact wrench, you should get one with a brushless motor as they are more effecient and produce less heat during operation. Extra Li-ion rechargeable batteries are also recommended!

Here’s an example of a cordless impact wrench readily available on Amazon.

Advantages

  • Ability to work in tight space
  • Portability

Disadvantages

  • Continuous use drains battery quickly
  • Heavier than corder and air versions
  • Most expensive

Impact Wrench Safety

Compared to other tools like saws and power drills, impact wrenches are relatively safer to use. But of course, there are precautions you must take as part of the standard safe working procedure.

Be aware of electric shock hazards while using a corded impact wrench. The cordless version may too pose risk arising from a damaged battery or shorted-circuites. They are not life-threatening like corded impact wrenches.

If you have very stubborn nuts or bolts then be sure to use the correct impact sockets. These sockets have thicker walls and are hardend and tempered to slightly lower hardness so that they avoid shattering. Always wear goggles to protect your eyes!

On average, impact wrenches produces approximately 90-100 dB of noise pollution. The hammer inside the impact wrench will produce loud noise so I strongly recommend wearing ear protection equipment such as safety ear muffs or ear plugs.

You may argue, but the mechanic at the car shop isn’t wearing any? Well, hearing protection is very important for anyone using an impact wrench for more than a couple minutes.

Commercial Impact Wrenches

If the intent is to acquire an impact wrench to use commercially, in a garage for example, care must be taken to ensure that the air supply will meet the demands of the impact wrench.

Commercial impact wrenches often have a 1/2″ or even larger drive. That means it’s a bigger wrench, and that means more air will be required to serve it.

If just acquiring the impact wrench, be sure to review the manual and if the tool did not come with one, make sure to get the online version of the manual. It is important to know how much air that air tool uses (normally measured in CFM) and at what pressure that air must be delivered (normally measured in PSI).

With that information, and knowing that each HP of compressor motor will deliver around 3-4 CFM of compressed air at 90 PSI, it is possible to determine if the compressor is big enough to run the impact wrench satisfactorily. Our What Size Air Compressor Do I Need For Impact Wrench? guide will answer all your questions regarding this matter!

FAQs (Frequently Asked Questions)

Can you use an impact wrench as a drill?

Yes, with the right adapters and drill bits you may be able to use your impact wrench as a drill. Some manufacturers will offer the adapters for their impact wrench so you can do some drilling, contact your manufacturer to find out if yours is suitable.

When should you not use an impact wrench?

You should never use an impact wrench with any attachment that isn’t impact rated. Also do not use impact wrenches on bolt extractors, they require slow steady pressure and not fast rotational impacts.

Is an impact wrench worth it?

If you work in an auto repair shop or if you’re incharge of mantaining machinery then yes an impact wrench is worth it. They make things a lot easier, and right now you may only use it for limited jobs, but having one will allow you to discover many more uses.

Can an impact wrench be run by any air compressor?

The short answer is yes, it can, as long at the pressure delivered by the compressor is greater than the minimum operating pressure of the impact wrench being used.

However, if the compressor doesn’t generate enough air flow to feed the impact wrench, even at the right pressure, eventually the impact wrench will lack sufficient air to run, and it will stop. That’ll happen usually in the middle of removing a nut!

Don’t stress it if that happens. Stop using the wrench and wait for the compressor to catch up, filling the tank up to cut out, and then when the compressor stops again, there will be enough pressure and flow to run the wrench for a while again.


If you have any questions about impact wrenches uses and how to use them, please leave a comment below, with a photo if applicable, so someone may help you!