What Is an Impact Wrench?

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Whether you are a mechanic, construction worker, or just handy around the workshop, you probably work with bolts, nuts, or screws from time to time. Whether you know it or not, you have probably used or seen an impact wrench before. So, what is an impact wrench? 

What Is an Impact Wrench? 

An impact wrench is a power tool mostly used for tightening or loosening large bolts, lug nuts, or rusted fasteners. It uses concussive rotation blows to produce more torque and drive more force to the output shaft. 

To put this into perspective, imagine you are trying to loosen a stubborn nut using a normal hand wrench. Most likely, the force your hand applies may not be enough to turn the nut. However, if you hit the wrench with a small sledgehammer, the repeated blows should be able to break the nut loose. 

The same applies to an impact wrench. Instead of merely spinning to turn the nut, an impact wrench uses a hammer mechanism to apply additional force when required.  

Set of drill bits

To clearly understand what an impact wrench is and how it works, it is important that you know the different types available. This will help you make a more informed decision when shopping for an impact wrench that’s right for you. 

Types of Impact Wrenches 

We can categorize impact wrenches into four types based on their power sources. These are: 

  • Corded Impact Wrenches: as the name suggests, a corded impact wrench uses electrical cords that you plug into an outlet socket to power them. They have a small electric motor that powers the hammer mechanism and transfers the motion to the output shaft. 
  • Cordless Impact Wrenches: These ones also use electric power yet they use rechargeable batteries instead of electrical cords. Cordless impact wrenches are more portable and flexible to use compared to their corded counterparts. 
  • Pneumatic (Air Powered) Impact Wrenches: These types of wrenches use a compressed air supply to power their rotor. They are relatively inexpensive compared to the electric wrenches. Pneumatic impact wrenches are also less prone to malfunctions because they don’t have any electrical parts. 
  • Hydraulic Impact Wrenches: Hydraulic Impact wrenches run on a fluid mechanism that uses a low-pressure hydraulic power to drive its motor. They are less commonly used and it is very unlikely that you will come across them.

So, which type should you choose? Depending on the power source that is more available to you, you can decide to go with either a pneumatic or electrical wrench. Also, if you want something portable and flexible to use, we recommend a cordless impact wrench. 

Man demonstrating what is an impact wrench

One thing that is very common across all the different types of impact wrenches is the hammer mechanism. This is what makes them powerful and preferable for high-torque tasks. So, it is only logical that you also understand exactly how the hammer mechanism works

How the Hammer Mechanism Works 

During a normal operation, the power from the rotor rotates the output shaft (anvil) which in turn turns the nut or bolt. However, when the anvil encounters resistance and the torque from spinning is not sufficient to turn the bolt or nut, the hammer activates. 

First, the hammer disengages from an engaging pin which causes it to connect with the anvil and rotate. The hammer then rotates at a higher velocity which results in generation of more energy. Consequently, the hammer transfers this additional kinetic energy to the anvil which causes it to exert higher twisting force and turn a stubborn nut or bolt. 

When the resistance is phased out and less torque is required, the hammer will disconnect from the anvil and go back to its original position until the output shaft encounters another resistance. 

Common Uses of an Impact Wrench

Like we have already mentioned, using an impact wrench for common household tasks would be absolute overkill. Instead, we recommend them for high-torque tasks that involve huge bolts and lug nuts. 

Here are some of their common uses: 

  • Removing lug nuts when changing car tires 
  • Assembling automobiles
  • Assembling and maintaining heavy equipment 
  • Manufacturing of machine tools 
  • Large-scale construction projects 

So, if you are doing some light tasks or simple DIY projects, you’d be better off with an impact driver than an impact wrench. This brings us to the question, what’s the difference between an impact wrench and an impact driver? 

Difference Between an Impact Wrench and an Impact Driver 

While both the impact driver and impact wrench employ the rotational hammer mechanism to make them more efficient, they are quite different in many ways. For starters, the impact driver is much friendlier to use and works better than most standard cordless drills. 

Impact wrench on a table

The main differences arise from the torque and usage. Here some notable differences between the two: 

  • Impact wrenches are heavier and more powerful than impact drivers.
  • Impact wrenches are for loosening and fastening sockets while impact drivers are mostly for driving screws. 
  • Impact wrenches are for industrial tasks like in the automotive industry while impact drivers are more suitable for common DIY projects around the home like basic car repair or home maintenance. 

Safety Tips When Using an Impact Wrench 

While impact wrenches are relatively safer to use compared to table saws and power drills, you still need to be careful around them. Keep in mind the following safety tips while using an impact wrench. 

  • When using an electric impact wrench, look out for any electric shock hazard. Although the cordless wrench is less dangerous compared to the corded one, it can also pose electric risks courtesy of short-circuits and damaged batteries. As a rule of thumb, you should always unplug electric wrenches when not in use. 
  • Wear protective goggles to protect yourself from eye injuries. 
  • Wear gloves, apply a firm grip on the impact wrench and always try to control the applied torque
  • Use ear protection. Most impact wrenches produce a lot of noise which might be damaging to the ear. According to CDC, exposure to more than 85dB (Decibel) of noise can cause hearing loss. As a comparison, most impact wrenches can produce up to 100 dB. 

Conclusion 

Hopefully, you now understand what an impact wrench is and how to correctly use it. Remember that this kind of wrench is not always suited for use with simple home projects. Instead, we recommend that you use the friendlier impact driver or hand wrench when doing regular DIY projects

An expert at home repair, remodel, and DIY projects for nearly 40 years. His first experience came in completely restoring an antique home. Completely redone from the inside out, and restored to its original form, the home is a featured design by renowned Southern California Architect Cliff May, considered to be the father of the California Ranch Home. Now Dennis spends his time on fine woodworking projects and tool comparisons.