Impact wrench makers quote two figures because the tool does two different jobs. Breakaway torque, also sold as nut-busting torque, is the maximum the tool can deliver in reverse to break a stuck fastener loose. Fastening torque is the maximum it delivers going forward, when tightening. The breakaway figure is always the larger one, so it is the one printed biggest. Neither number is a setting, and neither tells you what a particular fastener will actually receive.
That last sentence is the one that matters when you are standing in the aisle. A headline figure on an impact wrench is a ceiling measured under the maker's own conditions, not a promise about your car.
Breakaway vs Fastening Torque: What Each Number Means
Capri Tools, in its guide to impact and static torque (read on September 11, 2026), gives the clearest short definitions in the search results: nut-busting torque, "also called breakaway torque," is "the maximum instantaneous torque the tool can deliver in reverse to loosen a seized fastener," while working torque "is the sustained output during normal tightening." The same guide adds, flatly, that "nut-busting numbers are always higher."
In practice the two figures answer two different buying questions:
| Figure | Direction | The question it answers | When it matters to you |
|---|---|---|---|
| Breakaway / nut-busting | Reverse | Can this tool break my stubborn fasteners loose? | Removal jobs: rusted suspension bolts, seized wheel fasteners, crank bolts |
| Fastening / working | Forward | How hard can this tool drive a fastener? | Running fasteners down before final tightening by hand |
Most of what a home mechanic does with an impact wrench is removal. That makes the breakaway figure the more relevant of the two for most buyers, and it is also the one most prone to being read as more than it is.
Two Real Examples From Maker Pages
The pattern is easy to see on any major maker's product page. Two examples, cited to show how the figures are presented and not as recommendations:
- Milwaukee M18 FUEL 1/2" high torque impact wrench, model 2967-20. The maker's page (read on September 11, 2026) lists 1,200 ft-lbs fastening torque and 1,600 ft-lbs nut-busting torque, and says those figures apply "when paired with" a specific line of the maker's batteries.
- DeWalt 20V MAX XR 1/2" mid-range impact wrench, model DCF891B. The maker's page (read on September 11, 2026) lists 600 ft-lbs of max fastening torque and 800 ft-lbs of max breakaway torque. The asterisk on "MAX" leads to a note about battery voltage, not about how the torque was measured.
Both follow the same shape: a smaller forward figure, a larger reverse figure, and the reverse figure given more prominence. Both are also conditional. One depends on the battery fitted. Neither page, as read, explains the test that produced the number.
Why You Cannot Compare Headline Figures Across Brands
This is the part the buying guides skip. A torque figure means little without the method behind it, and impact wrench product pages rarely state the method.
Compare that with torque wrenches, where accuracy claims point at a named standard, ISO 6789, that defines how the test is done. On the impact wrench pages read for this article, the headline numbers carry qualifiers about batteries and voltage, but no statement of the joint, the fixture or the procedure used to measure them.
The practical consequences:
- Two brands' breakaway figures are not directly comparable. A higher number from one maker does not prove that tool breaks more fasteners loose than a lower number from another.
- One maker's own range is more comparable. Within one brand's lineup, the figures are presumably measured the same way, so the relative sizes are more meaningful than the absolute ones.
- The battery is part of the rating. A figure quoted with a large, high-output battery will not be what you get with a smaller pack from the same platform.
If a number looks too large to be real, the right response is not to decide whether it is true. It is to recognize that it was measured under conditions you will not reproduce, and to judge the tool on the jobs you actually have.
Why the Output Varies So Much in Use
Even with a method, an impact wrench does not deliver a fixed number. It hammers, and what each blow achieves depends on everything around it.
Capri's guide lists the variables: impact wrench performance "varies with air line pressure, hose length, ambient temperature, fastener thread condition, and lubrication," and "even on the same joint, consecutive trigger pulls can produce torque values that differ by 20% or more." It sets that against calibrated torque wrenches, which it places in a far tighter band.
For a cordless tool, add battery state of charge and the speed or mode setting. For an air tool, add the compressor's ability to keep up and the condition of the hose and fittings. Rust, thread damage and the stiffness of the joint change the result again.
This is why neither figure is a tightening setting. A tool whose output on the same joint moves by a fifth from one pull to the next cannot be trusted to put a specific figure on a wheel fastener, whichever number is on the box.
What the Fastening Figure Is Not For
The larger the fastening figure, the easier it is to overtighten something by accident. A tool rated far above what a fastener needs will keep hammering as long as the trigger is held.
Capri's guide makes the same point in the other direction: always match the working torque rating to the application, because relying on nut-busting torque for tightening will over-torque the fastener.
So the fastening figure is best read as a warning label as much as a capability. Critical fasteners, wheels above all, are run down gently if at all, and then brought to the figure in your own vehicle's service information with a torque wrench. This site publishes no torque figures for any vehicle. If you are choosing that tool too, the guide to which torque wrench to buy walks through it.
Using the Numbers to Choose a Tool
Here is how the two figures should, and should not, drive a purchase.
Start with the job, not the number. Write down the hardest removal job you realistically expect: wheel fasteners, suspension bolts, a crank pulley bolt. That tells you the size class you need, and size class tends to follow drive size, as explained in what each socket drive size is for.
Use breakaway to compare within a size class, from one maker. It is a reasonable way to rank a maker's own compact, mid-range and high-torque models against each other.
Treat a big headline number as a cost, not only a benefit. More output usually means more weight, a larger battery and more risk of overtightening. A mid-range tool that handles your hardest job comfortably is a better tool for you than one rated for jobs you will never do.
Distrust very large figures on unfamiliar brands. Without a published method, a large number is a claim, not a specification. The same kind of inflation shows up in socket sets, where a big number on the box says little about usefulness, a pattern explained in what a tool set's piece count really means.
Check what the rating assumes. If the page says the figure needs a specific battery, price that battery into the comparison.
| If you mostly… | Pay attention to | Do not over-read |
|---|---|---|
| Remove wheels and occasional suspension hardware | Breakaway figure within one maker's range, weight | The largest headline in the aisle |
| Run fasteners down before final tightening | Speed and mode controls that limit output | The fastening maximum |
| Tackle heavily rusted or large hardware | Breakaway in a high-torque class, and the battery it assumes | Cross-brand comparisons |
Where paying more buys real capability and where it only buys a bigger number is worked through in where buying cheap actually costs you.
FAQ
What is the difference between breakaway and fastening torque on an impact wrench?
Breakaway, or nut-busting, torque is the maximum the tool can deliver in reverse to loosen a stuck fastener. Fastening, or working, torque is the maximum it delivers when tightening. Breakaway is always the higher figure.
Why is breakaway torque higher than fastening torque?
Makers rate the tool separately in each direction, and the reverse, loosening figure is consistently the larger of the two on maker specifications. Product pages generally do not explain the test method behind either figure, which is why the numbers are hard to compare between brands.
Is a 1,600 ft-lb impact wrench rating real?
It is the maker's stated maximum under its own conditions. Milwaukee lists that nut-busting figure for its model 2967-20 when used with a specific line of its batteries. It is not what every fastener receives, and output in use varies with battery, joint condition and trigger time.
Can I use an impact wrench's fastening torque to tighten lug nuts to spec?
No. Output varies from pull to pull, so an impact wrench cannot deliver a specific figure reliably. Tighten wheel fasteners to the figure in your vehicle's service information with a torque wrench.
