Frequently Asked Questions


What is the difference between cordless drill and impact driver?

The short answer:
A drill/driver is the tool most people are familiar with. It can accept drill bits or driver bits of all sizes. Drills have a single type of operation: smooth rotational action.

An impact driver provides a higher speed rotational action. In addition it provides much higher torque by means of thousands of impacts (!) each minute on an internal mechanism. This operation, while noisy, allows a low-recoil way of driving fasteners with much higher torque than a drill.

Read more about impact drivers vs drills


What is the difference between an impact driver and an impact wrench?

Not a lot! The most obvious difference is that, generally, an impact wrench can provide much higher torque than the impact driver. For example, a strong driver can reach around 1500 in-lbs of torque, while an impact wrench can deliver more than 300 ft-lbs (or 3600 in-lbs)

Impact drivers are targeted more toward fasteners like screws and smaller bolts, while the wrench can be used for much larger diameter bolts and nuts (like car lug nuts).

Read more…


When would I use an impact driver?

Whenever you have a fastener to fasten. Screws of all kinds are one of the most popular kinds of fasteners, although lag bolts of all sizes are also driven with impact drivers as well as nuts or anything that needs turning. You can even use a socket attachment and drive an eye-bolt or l-hook.

Trying to drive a long screw into hard wood with a drill puts lots of strain on your wrists as you provide a counter force to the rotation. And it’s easy to cam out and strip the screw head. With an impact driver, the hammering action inside the tool creates the rotational force, and there’s very little recoil to push against. And since there’s a bit of downward force applied, the bit is less likely to cam out.

With the extra power afforded, lags drive through thick wood with ease. And drilling large holes with a spade bit are a snap and won’t drain your battery (unlike with a cordless drill).

Check out 10 more ways to use your impact driver.


What is a brushless impact driver?

‘Brushless’ refers to the type of motor used to power the impact driver.

In a standard motor, the ‘brushes’ are used to pass electricity to the spinning rotor. They eventually can wear down and reduce tool performance.

Brushless motors are built in a way that doesn’t require an electrical connection to spinning parts. This reduces friction and heat while increasing tool life, among other things.

Read more here.


What is the difference between 18 volt and 20 volt drivers? What about 10.8 volt and 12 volt?

The move to 20 volt terminology is mainly about marketing! When a battery is fully charged, it has a slightly higher voltage rating than if you measure that battery while it’s working.

If you look close, many of the tools that say ’20V’ often have a small disclaimer stating that is the Max or Peak voltage, and operating voltage is lower.

When you are at the store, and looking at mostly comparable tools, which would you rather have? An little 18v Makita or the huge 20V Max* DeWALT? At least, that’s what they are banking on.

This doesn’t mean you can necessarily use your old 18v batteries however – in many cases, such as with DeWALT, they changed their battery format, form-factor, and electronics as well as the marketing.


Can you drill holes with an impact driver?

Of course! An impact driver usually has high rpms – in fact, cordless drivers beat out many cordless drills in the speed department. Some impact drivers don’t have great control of the low-end speed, however, so it can be a bit tough to start holes as precisely as a drill. On the other hand, the higher torque means large holes from spade or auger bits can be chewed out with little effort.

And, if you don’t want to buy a whole second set of hex-shafted drill bits to fit into the typical 1/4″ chuck, a number of manufacturers offer a drill chuck attachment. See our Accessories page for more info.


Can I use an impact driver to take off lug nuts?

It may be possible to take off a lug nut, but you will need a socket attachment to fit.
Typical lugs are supposed to be tightened between 70 and 120 ft-lbs, depending on the car and the wheel/lug size. This translates into 840-1440 in-lbs, which is how impact drivers are typically rated. Going by the numbers, a larger 18V driver should have little trouble in most cases.

However, in practice, many dealers/mechanics over-tighten the lugs. And even correctly torqued nuts can begin to seize due to rust, dirt, and time. Finally, for the reasons explained below, you can’t directly compare those torque values. Unless you have one of the more powerful impact drivers with the right attachments, you may run into trouble. In that case, try loosening the nut with a large breaker bar, then switch to the impact driver to quickly unscrew it the rest of the way.

If you plan on taking off lots of lugs, you should think about getting the impact driver’s larger cousin, the impact wrench.


Why don’t the impact drivers have as high a torque in tests as their stated rating?

There are a couple of reasons why a test of the max torque of your impact driver might fall short of the manufacturer’s specs.

First is something referred to as breakaway torque. Thanks to static-friction, a nut requires a much larger force to initially loosen it than it took to fasten it. This is why tests in which people use a torque-wrench to tighten a nut often have extreme results stating X driver has 50% or less torque than it’s supposed to.

One source lists the static friction of non lubricated steel-on-steel to be 30% higher than kinetic friction. Although in practice, other things like rust, dirt/dust, or manufacturing artifacts can all change the ratio.

Secondly, in most cases there will indeed be a drop from the stated specs. The manufacturers usually get their numbers in perfect conditions and fully powered batteries. However, a huge (50%) drop would likely mean that either someone got a lemon (it happens!) or someone is using faulty test procedures.

That’s not to say you can’t trust people who are doing side-by-side comparisons. You don’t need math to see one tool work better than another. But it’s not a bad idea to be skeptical of any numbers they come up with, especially if they seem extreme.


Which is better for driving deck screws – an impact driver or a drill driver/screw gun?

While this can be debated, many professionals agree that an impact driver is better for dealing with a deck. We’d say a majority, but we don’t have any data to back it up just anecdotal evidence!

There are many reasons given, including:

  • lighter tool means less fatigue
  • more screws can be fastened between charges
  • less cam-out on all screw types means work moves faster (this is a big one!)
  • easy to quickly swap to a drill bit if you need pilot holes near edges

Is there an impact driver I can use for fastening to concrete?

Of course. In fact, depending on the application, almost any impact driver can be used for concrete applications. In practice, however, 18v models will have the power to install multiple fasteners without wearing down too quickly.

You can even drill the pilot holes into the concrete with an impact driver! Note that an impact driver does NOT provide any pounding action, like a hammer drill. This means that your drilling will progress much slower, but if it’s all you have you can get the job done. Be sure to use a masonry bit!


What is a hand impact driver for? How does a hand impact driver work?

A hand or manual impact driver is for breaking over-tightened or rusty screws and nuts free. They work by converting a sharp smash from a hammer into a shock-torque impulse that can loosen the most stubborn fasteners.

Hand impact drivers share some underlying aspects with cordless impact drivers, but in general they are for very different applications.

Read more here.


What is the difference between chrome vanadium and chrome moly?

These steels are different alloys that have been created for different purposes.

Chrome vanadium is very strong and hard, but it’s more brittle than chrome moly.

For this reason, you will often see hand tools made of chrome vanadium, but quality impact-ready tools (like sockets or bits) made with chrome moly. The softer metal can absorb more impacts before shattering.

Remember that manufacturing technique is just as important as the metal used, so beware anything that seems TOO cheap.

See here for more on different steels you might run across.


How do I convert ft-lbs to in-lbs?

This one is simple enough to do – just 1 operation on a calculator.
To convert from foot-pounds to inch-pounds, you simply multiply the ft-lb value by 12.
To go from in-lbs to ft-lbs, you do the opposite: divide the in-lbs value by 12.
Some examples:
  1400 in-lbs -> 1400/12 == 116.67 ft-lbs
  100 ft-lbs -> 100 * 12 = 1200 in-lbs


Can an impact driver be used for screwing in drywall?

Of course! In fact, installing drywall is a great use for an impact driver. Not only are they lighter than drills, they are faster too.

However, impact drivers aren’t known for their finesse. It’s super easy to over-drive screws when working in soft materials. It would be very wise to use a drywall-bit to prevent over-driving of the screws since an impact driver is so quick. (Such as these dimplers from DeWALT.)


What’s the best 18 volt impact driver on the market?

It depends on what you intend to use it for, and what your budget is. There’s no one right answer for everyone! Head on over to our Buyer’s Guide and see what’s best for you!


What’s the easiest way to compare the drivers?

Use CIDHQ’s Impact Driver Comparison Tool, of course! You can pick any impact driver you see, anywhere on our site, and add it to your Comparison Tray. Then when you are ready, click the Compare button and see a side-by-side comparison of detailed specs.

Have any more questions? Ask them below!

2 Comments

  1. Larry B
    Posted June 24, 2012 at 5:25 pm | Permalink

    I think you need to check your math. The following is incorrect:
    How do I convert ft-lbs to in-lbs?

    . . . .
    Some examples:
    1400 in-lbs -> 1400/12 == 166.67 ft-lbs

    Someone dropped a digit: that should be 116.67

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