What Is An Impact Wrench- Understanding Its Types , Uses and Size

1. Introduction of An Impact Wrench

During your last visit to the auto shop, you might have noticed the mechanics using impact wrenches to remove wheels from cars. They’re also used to remove bolts from heavy machinery and to fasten studs on construction sites. But have you wondered what goes on inside an impact wrench, and how it derives its amazing rotational power? Wonder no further, because today, we shall explain everything you need to know about impact wrenches. By the end of this article, you will be familiar with the many types of impact wrenches and their application across a wide range of industries. So without further ado, let’s get started, shall we?

2. What Is An Impact Wrench And How Does It Work

If you’ve ever hammered down on a socket wrench or breaker bar while trying to pull off a stubborn lug nut from your car wheel, you’ve simulated the same type of action that takes place inside an impact wrench. An impact wrench, simply put, is a power tool designed to deliver large amounts of torque in the form of rapid pulses, each simulating the strike from a hammer. In fact, if you open up an impact wrench, you’ll find that its head contains a rotating hammer and an anvil.

The hammer is spring-loaded and cammed, so it spins freely after delivering each strike. An impact wrench is optimized for torque rather than RPM, which is why in the electric models, you’ll often find a gear reduction mechanism between the motor and hammer. And, we also have pneumatic and hydraulic impact wrenches, which use a similar hammer + anvil mechanism but obtain their power from pressurized air or hydraulic fluid instead of an electric motor. 

3. Types of Impact Wrench

Depending on the power source and intended application, there are several types of impact wrenches with fundamentally different designs and internal components. Let’s take a look at some of them.

Pneumatic Impact Wrenches

Firstly, we’ve got pneumatic impact wrenches, which are commonly found in auto shops as they work off the same air compressor and tank that is used to power other tools like drills, die grinders, spray guns, and sandblasters. A pneumatic impact wrench is an essential tool for every mechanic as it simplifies the process of swapping out tires. Impact wrenches can also be used to open up engine blocks and transmissions.

But how do pneumatic impact wrenches work? Simple, they use a pneumatic motor instead of an electric one. In a pneumatic motor, there is a rotor that acts like the turbine in a windmill. Its job is to “catch” the pressurized air flowing on top and convert that force into rotational motion, which is then transferred via a shaft to the hammer mechanism. There is also a valve that changes the direction of airflow within the motor to make it spin in reverse.  

Electric Impact Wrenches

Electric impact wrenches are powered by electric motors and are divided into two subcategories- corded and cordless.

Corded Impact Wrenches
Corded impact wrenches are cheaper and simpler, since they use universal motors with commutators. For sustained all-day use, cordless tools are a better choice as they don’t rely on batteries, which drain away over time. Instead, they get their power from the wall. The downside to this is that corded impact wrenches can’t enjoy the performance benefits offered by modern-day battery technology, which can push a lot more current than what you get from the wall. And your workspace will always be limited by the length of the cord.

Cordless Impact Wrenches
Cordless impact wrenches are more expensive, but also more efficient and versatile. You can take them anywhere and get into any spot without worrying about a cord getting tangled up. Good cordless impact wrenches, like our Yofidra ½” 1000Nm cordless impact wrench, also use brushless motors that run cooler and generate less friction, resulting in a longer lifespan and more power. With a cordless impact wrench, the quality of the battery is just as important as the tool itself, which is why our tools can take 18V Makita batteries that are some of the best in the entire industry.

Hydraulic Impact Wrenches

Hydraulic impact wrenches are exclusive to hazardous zones and industrial applications where an enormous amount of torque is needed, and you can’t afford to have any sparking because the atmosphere contains combustible gases or flammable liquids. You see hydraulic impact wrenches in mines, oil rigs, and undersea work zones. They are often paired with specialized non-sparking, non-magnetic sockets and come in drive sizes 1-1/2” or bigger to fasten and remove truly massive bolts. Just like pneumatic impact wrenches, hydraulic impact wrenches use a pipe that carries compressed fluid to power the motor. But the pressures are MUCH higher, in the order of thousands of psi.

Specialty Impact Wrenches

Sometimes you need heavily specialized tools for a particular job. That’s where specialty impact wrenches come in, and there are two main types.

Mini Impact Wrenches
Used to fasten smaller bolts, mini impact wrenches typically come with ¼” drives and are designed for use in restricted spaces. These are small and light, plus they’re a lot cheaper than a ½” or even 3/8” impact wrench.

Heavy-Duty Impact Wrenches
Heavy-duty impact wrenches are on the opposite end of the spectrum from mini impact wrenches, and use 1” or bigger drives for industrial applications. They are used to fasten and remove really big bolts, like the ones you find on railroad tracks or shipping cranes. Heavy-duty impact wrenches are usually pneumatic or hydraulic, although some can even be gas-powered, using 2-stroke motors similar to what you find on a chainsaw.  

4. What Is An Impact Wrench Used For

As we’ve seen, impact wrenches come in a wide variety of sizes and can be powered by everything from electricity to pressurized hydraulic fluid. And there’s a reason for this diversity in designs- impact wrenches are used in a multitude of applications, basically anywhere people need lots of torque to fasten or loosen stuff. So let’s take a look at some of those applications.

Automotive Industry

The most obvious use case for impact wrenches and probably also the most ubiquitous one, is in the automotive industry. Here, the humble ½” impact wrench is used for just about everything- from removing lug nuts to taking apart entire powertrains. While most auto shops still use pneumatics, because they already have the supporting equipment for that ecosystem, many of the newer shops are transitioning to cordless for the increased flexibility and ability to access tighter spaces. With an impact wrench, mechanics can easily remove rusted chassis and suspension bolts or open up an engine block. For crank bolts and big rig lug nuts, you’ll want a high-torque model, but otherwise- there’s no bolt on a vehicle that a 1000Nm  torque wrench can’t handle. If you have an impact wrench with a 1” drive, you can also repair diesel engines on farm and construction equipment like tractors and skid steers.

Construction and Heavy Machinery

Construction crews will use impact wrenches to install or remove scaffolding. They are also used to drive anchors into concrete and for tightening flange bolts on large pipes. Any task that involves large bolts and requires lots of torque can benefit from the application of an impact wrench.

Beyond structural work, impact wrenches can also be used to assemble and disassemble heavy machinery and its associated components. For example, let’s say you’re doing some renovation on a commercial property and one of the cranes has a few frozen bolts. An impact wrench can easily remove these bolts in a matter of seconds.

Impact wrenches are also used for routine inspections and maintenance of construction equipment like backhoes, excavators, skid-steers, forklifts, compactors, loaders, and more.

Manufacturing and Assembly Lines

On an assembly line, impact wrenches are used to fasten bolts and ensure torque consistency. Not to mention, they’re dramatically faster than torquing each bolt by hand. Impact wrenches can be found in both automotive and aerospace manufacturing.

Home Improvement and DIY Projects

On the home improvement front, few tools beat a cordless impact wrench in terms of value for money. With just one tool, you can secure fasteners across many different materials and drive even the heaviest bolts into structural beams. Whether you’re laying down a new fence or rigging up some scaffolding, you’ll need an impact wrench. If you’re installing a new deck or gate, you’ll need to drive lots of lag bolts, and an impact wrench can come in handy. It will also remove the blades from your lawnmower, which are usually stuck in there pretty tight due to all the mud and grime that gets into the bolts.

Maintenance and Repair Services

Professionals use impact wrenches to drive in bolts for installing new HVAC systems, and to remove old bolts or fittings that are rusted tight after years of exposure to moisture. Sometimes, the HVAC system needs to be secured to a concrete or steel surface, and there’s no better way to do it than with an impact wrench. Impact wrenches are also used to remove old fittings in plumbing and electrical work.

5. Choosing The Right Impact Wrench Size For Specific Scenarios

Impact wrenches come in many different sizes, and generally speaking, larger drive sizes mean more power. But bigger isn’t always better. For most people reading this, we recommend a ½” impact wrench as it will let you work on any part of your car with ease. You can change flats and do tire rotations within minutes if you have a ½” impact. But for industrial jobs and maintenance of heavy machinery, a ¾” or 1” drive might be needed.

Understanding Impact Wrench Sizes

All impact wrenches have a “drive”, which is a square-shaped bit at the front that has some kind of locking mechanism for the socket. The width of this drive is what we refer to when we talk about impact wrench size. It can range from ¼” to 1” and beyond. The most common drive sizes in the consumer market are ¼”, 3/8”, ½”, ¾”, and 1”. You must always match up your socket size to that of the drive on your impact wrench. For example, if you have a ½” impact wrench, you’ll need a ½” socket. And this has to be an impact-rated socket; regular ones are too brittle and will shatter. Impact-rated sockets are made from a Chrome-Molybdenum Steel alloy and have a cross hole in the handle that latches onto the retaining pin in the impact wrench drive.

Automotive Repair and Maintenance

For automotive repair and maintenance, you’ll want a ½” impact wrench. Unless you’re working on big rigs and diesel-powered farm equipment, in which case a ¾” might better suit your purposes. For engine and transmission work, you can use the same ½” or 3/8” impact, but make sure it’s rated for at least 1000Nm of torque if you plan on removing crank bolts. Sometimes, you’ll have to use extension bars and swivel sockets to reach suspension components like the upper control arm bolt. This requires a lot more torque than usual because an extension bar will cut down on your torque output. A ¼” compact model is good for reaching into tight spaces, but you won’t get much torque out of those; they usually top out at 250 to 300Nm. Cordless is the best, as you won’t get tangled up in wires or air pipes, and they perform just as well as the most powerful corded or pneumatic wrenches, thanks to advances in motor and battery technology. Plus, you can take the cordless wrench with you on a drive to quickly change out flats on the road. You can’t do that with a corded or pneumatic wrench.

Construction and Heavy Machinery

Construction workers prefer at least a ½” drive, with high torque output. They generally go with pneumatic for sustained heavy-duty applications, although some jobs can also be done with a cordless model. For fastening and removing large bolts on heavy machinery, a 3/8” or 1” drive is required. These are the bolts you find on cranes, elevators, semi-trucks, industrial generators, large hydraulic pumps, and presses.

Home Improvement and DIY Projects

For occasional home improvement and DIY work, we highly recommend a cordless impact wrench with a ½” drive, as it will have more than enough power to drive your bolts. And, the best part is you can use the exact same tool for all your car maintenance work. If you do lots of furniture fittings and plumbing, you can get a separate ¼” or 3/8” cordless impact wrench that is more specialized for these tasks. Make sure it has a light and is as compact as possible.

Industrial and Manufacturing Settings

Industrial settings demand heavy-duty torque and sustained power output day in, day out. Since recharging means decreased productivity, assembly lines equip their workers with corded or pneumatic tools. On automotive lines, you’ll find plenty of ½” impact wrenches. In the aerospace sector, ¼” impact wrenches are used for precision tasks that don’t require as much torque. In the mining and oil sectors, a 1-1/2” hydraulic impact wrench is a common sight. So it all depends on the industry and specific application.

Special Considerations

With impact wrenches, there can be such a thing as “too much power”. Hence, you must bring the right tool for the job; otherwise, you risk over-torquing components and causing premature wear. A ¼” impact wrench can deliver 100 to 150 ft/lbs of torque, which should be enough for most DIY home improvement stuff, but sometimes you’ll need a little extra juice for stubborn lag bolts and anchors that refuse to come out. Then, you can step things up a bit to 3/8”, which carries 200 to 300ft/lbs of torque. These are general figures and not representative of any actual models or brands; they’re just here to give you a rough estimate of how much power you can expect from each impact wrench.

A ½” impact wrench can have a very wide torque band depending on the build quality and battery type. Some produce under 400 ft/lbs of torque while others go beyond 700 ft/lbs. If you want to fasten bolts to a precise torque spec, always go with a torque wrench, as impact wrenches aren’t precision tools. However, what they’re very good at is removing tightly fastened bolts.

On the other hand, if you just want to drive in lag bolts, you don’t need to be too precise with your torque numbers. Depending on the material you’re working with, you’ll need more or less torque. So, for example, driving a bolt into wood requires less torque than driving it into concrete.

6. Conclusion

We hope this guide helped you understand what an impact wrench is and how it works. It’s hard to overstate the importance of impact wrenches in the automotive and construction industries. Thanks to the advances in cordless technology, the average consumer can also experience the productivity benefits of owning an impact wrench because modern cordless wrenches are comparable in power to old pneumatic and corded models.

7. FAQs

Q: Can I use a cordless impact driver to remove lug nuts?
A: Yes, a cordless impact driver can be used to remove lug nuts with a ¼” to ½” socket adapter. But it will struggle with lug nuts that are tightly seated, since it lacks the torque output of an impact wrench.

Q: How much torque does a cordless impact wrench need to remove lug nuts?
A: Assuming the lug nuts are tightened to spec and the tires are rotated regularly, you shouldn’t need more than 150 ft/lbs of torque on a car. Semi-trucks require more than 500 ft/lbs. But if the lug nuts are seized in place due to rust or swelling, you might need as much as 700 ft/lbs.

Q: How many ft/lbs to tighten lug nuts?
A: Passenger vehicles require no more than 90 to 150 ft/lbs of torque on their lug nuts. You should always use a torque wrench and refer to your car’s user manual for the precise figure. Tighten the lug nuts in a star pattern for maximum consistency and reliability.

Q: What is the correct torque for lug nuts?
A: Between 90 and 150 ft/lbs, as measured by a torque wrench. Don’t use impact wrenches to fasten lug nuts.

Q: Are cordless impact wrenches as powerful as corded ones?
A: Modern cordless impact wrenches come with high-current output batteries which can surpass the amount of power a cordless wrench gets from a 110V outlet. As a result, not only do modern impact wrenches match corded models in performance, but they can also even exceed them.