- Published 8 Jan 2025
- Last Modified 8 Jan 2025
- 6 min
A Guide to Impact Wrenches
What is an impact wrench used for? Impact wrenches are power tools for tightening or loosening even the toughest fastenings. This guide explains what impact wrenches are, how they work, the different types of impact wrench on the market, and how to use them safely.
Reviewed by Karl Ralph, Technical Support Engineer (December 2024)
If you’ve ever wondered what that whirring noise is in the pit lane when a Formula One pit crew is changing the tyres on a car, this guide is for you. That distinctive sound is made by an impact wrench – a heavy-duty power tool designed to tighten or loosen fasteners.
Read on to learn about what impact wrenches are, how they work, and the different types of impact wrench on the market.
What Are Impact Wrenches?
Got a socket, nut, or bolt that just won’t budge? Time to turn to an impact wrench. These tools tighten or loosen even the toughest fastenings by generating a high level of torque for socket wrenching with minimal effort. As well as motorsport, impact wrenches are widely used in automotive manufacturing, garages, equipment maintenance, product assembly, and construction.
Impact wrenches come in a range of sizes and are modelled on a standard socket set, from a quarter of an inch up to three and a half inches. They offer increased productivity because of their speed and make loosening and tightening nuts easier. If other methods such as breaker bars or ratchet wrenches have failed, the impact wrench can often shift even the most stubborn of fasteners. Impact wrenches are used for both assembly and disassembly.
How Does an Impact Wrench Work?
You’re probably asking, how does an impact wrench work? Impact wrenches typically feature an electric or air motor which converts a horizontal, hammer-like motion into a twisting force that is delivered to the nut or bolt in short bursts. The motor accelerates to store energy and then rapidly connects to the output shaft to generate high-torque impact. (These are known as ‘torque peaks.’) The mechanism spins freely and does not stay locked. This creates a huge level of force which enables even very tough nuts and bolts to eventually loosen. Impact wrenches are specified for different levels of torque. The higher the torque level, the more powerful the impact wrench.
What is the most powerful impact wrench? Some impact wrench types generate as much as 610 Nm, but you won’t need this amount of torque for most jobs. Many impact wrenches are powered by compressed air, but there are also wired electric and battery-powered versions on the market, which are useful if the engineer is travelling to sites where a source of compressed air is not available. The disadvantage of this latter type is that it requires recharging and is subject to battery life constraints.
What is an Impact Wrench Used For?
What is an impact wrench used for? Impact wrenches come into their own whenever powerful rotational movements are required. This could be for a DIY project such as creating a wooden deck where long screws need to be driven into wood. Impact wrenches are also used at garages and workshops everywhere to change tyres, not to mention on construction sites to drive screws into metal.
If you’re wondering how to use an impact wrench, read on for the advantages of each type.
Impact Wrench Types
Impact wrenches come in a range of types. You first need to consider what is a good torque for an impact wrench when it comes to the job at hand. Then, depending on what you’re doing, you may want to go for a:
Cordless Impact Wrench
Cordless impact wrenches feature the convenience of cordless operation. They can be readily transported and used at locations where there is no compressed air supply. Battery life is a consideration, however. It’s important to consider recharging times and how these might impact your operation, and the longevity of the battery.
Air Impact Wrench
Air impact wrenches need a compressor to work but are more powerful than battery versions. The force they apply depends on the pressure generated by the compressor. (90 to 120 PSI is a good level to aim at.) More torque can be generated by applying more pressure.
Electric Impact Wrench
Electric impact wrenches come in either cordless versions (see above) or plug into the power supply to operate. The latter, like cordless battery-powered versions, don’t require a source of compressed air to operate. However, there are some sectors where electric impact wrenches can’t be used because of safety issues, such as oil and gas, petrochemicals, and mining.
Right Angle Impact Wrench
Right angle impact wrenches are compact designs. They operate at a 90º angle and are great for tightening and loosening fastenings in hard to reach and confined areas. Some right angle impact wrenches are also extendable, which helps them to access tricky places.
Impact Wrench vs Impact Driver
When it comes to considering which impact wrench or driver to use, it’s important to remember the difference between impact driver and impact wrench tools.
While impact wrenches are designed to loosen or tighten nuts and bolts, impact drivers are designed to drive screws and fasteners. Do you want to know how to tell them apart? A straightforward way is looking at the driver. Impact drivers usually have a quarter-inch hex collet, but impact wrenches have a half-inch square drive.
Impact Wrench Safety Checklist
Safety is paramount when using an impact wrench. Here are some of the factors to consider on your impact wrench safety checklist:
- Review the impact wrench manual before using.
- Inspect the wrench for damage or missing parts. This includes inspecting the air hose and fittings if using an air compressor.
- Wear safety glasses. Since impact wrenches are noisy, hearing protection must also be worn.
- Tie back hair, don’t wear loose-fitting clothing, and remove jewellery.
- Operate at the pressure specified by the manufacturer if using an air impact wrench.
- Only use impact associated tooling, impact sockets and impact driver bits.
Also remember that impact wrenches cause vibration. If you experience pain or discomfort in your hands and arms due to vibration, stop what you are doing and seek medical assistance.
Overall, impact wrenches are safe and immensely useful tools in the technician’s armoury. Bear these simple precautions in mind, and you’ll soon be swiftly loosening nuts and bolts with the speed and efficiency of an F1 crew.
Did you know RS also carries a wide range of power tools for soldering and welding? Browse it now.
