Are Torque Sticks Accurate?

Two answers go around. Some sellers say a stick will hit the lug nut spec every time, no torque wrench needed. Tool blogs say it lands within 2 to 5 ft-lb of its rating. Neither one has a maker's number behind it. The makers that print instructions say something else: the stick sets a ceiling, your setup decides where under that ceiling you land, and a torque wrench does the final step. Below, five makers' documents side by side, one 100 ft-lb wheel worked through, and where the 5 ft-lb figure really comes from.

What a torque stick is

A torque stick is a steel extension bar that goes between an impact wrench and the socket. Makers call it a torque limiting extension or a torque extension bar, and each one carries a rating, such as 80 or 100 ft-lb, and a color.

It works by twisting. An impact wrench drives a fastener with rapid blows from a hammer inside the tool, and while the nut spins freely the bar passes those blows straight through. Once the nut seats and resists, the bar starts to wind up and spring back, like a torsion spring. That twist soaks up energy that would otherwise reach the nut.

Nicholas Bush of ACDelco Auto and Equipment Tools put it this way in a tech tip for Vehicle Service Pros. Torque sticks "limit applied torque by absorbing input torque through torsion deflection, or twist." Then he adds the catch: "there are many variables that can affect the torsional deflection (absorbed torque) and the applied (delivered) torque. These can lead to inaccurately applied torque or variations in applied torque."

Two terms carry the rest of this page:

• Rating is the number engraved on the stick. It is a design value, set when the bar is machined, not a measured result on your gun.
• Tolerance is how far the real torque may sit from the rating. A torque wrench prints one, and no torque stick maker checked here does.

What five makers print

These are the documents that could be fetched for this page. Ken-Tool also sells torque extensions, but its product pages refused automated reads, so it is not in the table.

The tolerance column is the answer to the question this page is named for: five makers and five blank cells.

The last two columns are where the makers split. Matco and Astro print the same instructions, almost word for word, and they are the most complete of the five. Both say the sticks are made "to limit torque delivered to lug nuts when using an impact wrench" and "are not designed for reaching the final torque specification." Both end on the same line in capitals: "ALWAYS USE A TORQUE WRENCH AFTER USE TO REACH FINAL TORQUE SPEC."

King Tony's catalog prints its ratings under the heading "Max. torq." That is a ceiling, in the maker's own word, not a target. Its steps end with "Check the actual tightening torque value by torque wrench" and then "Adjust air pressure or torque value according to the result of above."

GearWrench says its bars are "designed to limit the amount of torque applied to a fastener when using a calibrated impact wrench." The page does not say how to calibrate the gun, and prints no tolerance.

Capri goes furthest in the other direction. Its page says the five ranges mean "you'll hit manufacturer specs every time without an expensive torque wrench." It prints no tolerance to back that up. This is the claim that the Matco and Astro instructions contradict, and it is where the "no torque wrench needed" answer comes from.

Why the stick cannot know your torque

Matco puts the core of it in one sentence: the set "is calibrated from the factory and therefore it is static. Because the torque level is determined when machined, it cannot change and the user must calibrate how they use, and what they use with the extensions below to obtain the desired torque level."

The bar is fixed, but everything driving it is not. The Matco and Astro instructions name what moves the result:

IPM is how many blows the gun's hammer lands each minute. On why it matters most, Matco says a gun with a higher IPM "will not allow a torque limiting extension to rotate back and fight against the impact gun." Put simply, a faster gun gives the bar less chance to rotate back between blows.

Air pressure at the tool is not the number on the regulator. A long or narrow hose drops pressure while the gun runs, as worked through in whether 3/8 hose is big enough for a 1/2 in impact. Change the hose, its length or the regulator, and you have changed the setup the stick was matched to.

King Tony gives the most specific starting point of the five. Set the air to 0.6 MPa (90 psi), and adjust the gun's own torque to between 190 and 210 N·m (140 to 155 ft-lb). Then check the result with a torque wrench and adjust the air from there.

How the makers tell you to calibrate

Matco and Astro print the same three steps. Here they are in order, in plain terms:

1. Torque. Use a torque wrench to bring a lug nut to the value you want to limit to. Mark the nut and the hub or wheel face at the same spot with chalk or a paint pen. Remove the nut with a breaker bar. Pick the stick whose rating is closest to that value.
2. Test. Set the impact to its middle power level. Run the nut on with the stick until it seems to stop turning, "usually 1-2 seconds." Check the marks. If the nut stopped short, raise the power and try again. If it went past, lower it. Once it hits the mark reliably, always use that air pressure and power setting.
3. Adjust. If the gun cannot hit the mark at any setting, and you cannot change the air supply, try a different socket (more mass raises the torque), a different gun, or a shorter burst.

A fourth step covers a stick that will not line up. Matco's example is a 90 ft-lb stick that is "always 10 ft. lbs. low with your set-up." In that case, it says, "it would not be uncommon to need to use the 100 ft. lb. extension from then on, as long as the results are consistent."

That example is worth reading closely. A miss of 10 ft-lb on a 90 stick is 11 percent of its rating. The makers do not treat it as a defect, but as a setup to work around by changing sticks. What they want is the same result each time: "Consistent repeatable results are the intention of the product in order to ensure it does not go over a certain value."

A 100 ft-lb wheel, worked through

Take a car whose lug nuts are specified at 100 ft-lb (136 N·m). Suppose you have the Matco set, an air impact and a 1/2 in click torque wrench.

Pick the stick. Matco answers this directly: "if you're wishing to torque a vehicle's lug nuts to 100 ft. lbs., the 80 or 90 ft. lbs. extension might be a good choice to quickly install the wheels on the car and ensure in doing so, you will not exceed the recommended torque level."

So the stick for a 100 ft-lb spec is not the 100 stick, but one or two steps below it.

Run the nuts on. With the 90 stick, at the air and power setting you found in the chalk test, each nut runs on in a second or two. The aim at this stage is to stay under 100, not to reach it.

Finish by hand. Lower the car, set the torque wrench to 100 ft-lb, and bring each nut to the click in the pattern the vehicle maker gives.

Read the windows side by side.

The 100 ft-lb setting is two-thirds of the way up a 20 to 150 ft-lb wrench. That puts it inside the 20 to 100 percent span the ±4 percent covers. The stick has no such span, because it has no window at all.

Now suppose you skip the torque wrench and run the nuts on with the 100 stick instead. The instructions give you no number for where those nuts end up. Matco's own example shows a setup can sit 10 ft-lb under on a 90 stick. Its use table allows a 100 stick on a 105 job. Neither of those is a window. And Matco says using the stick "as the only method to fasten bolts and nuts with a required torque value is not recommended and the user does so at their own risk."

Where "plus or minus 2 to 5 lb" comes from

The figure turns up on tool blogs and in forum answers. Garage Tooled, reviewing a Capri set, says sticks are "accurate to within +/- 2-5 pounds of their rated capacity." It gives no source, and none of the five makers here prints it.

The 5 does appear in the Matco and Astro documents, but as something else. Both say: "Because the purpose of these tools is to limit torque, some extensions can be used for other applications within 5 ft. lbs. above their rating." Then they print which jobs each stick is for:

Read closely what that table says. A 100 stick may be used on a job whose spec is 105, because the stick will stay under 105. It is a rule for choosing a stick, and it only runs upward. It says nothing about how far under the rating the stick may land, so it is not a tolerance.

That is why the folk figure persists. It borrows the one 5 ft-lb number in the makers' documents and turns a use rule into a precision claim. The instructions themselves go the other way: they tell you to measure your own setup with a torque wrench, because the stick cannot promise a number.

Even the engraving is rounded

King Tony engraves each bar in both N·m and lbf·ft, and the two numbers do not always match. Converted at 1 N·m = 0.7376 ft-lb:

The two engravings on the 200 N·m bar sit 2.5 ft-lb apart. That is a rounding gap, not a test result, but it shows how loosely the numbers on a stick are meant to be read. A torque wrench has a scale and a printed window. A torque stick has a label.

Where this answer stops

This page reads what the makers print. Nobody tested a stick for it, and it gives no measured figure for any stick on any gun or at any air pressure.

Cordless guns. GearWrench says its bars work with cordless and air impacts. No maker publishes how a stick behaves on a given cordless model, and cordless wrenches also run modes and IPM ranges far from an air gun's. Makita's TW003G, for one, lists 0 to 2,400 ipm, among the figures in nut-busting vs fastening torque. By Matco's own account IPM is the main factor, so a stick set up on one gun says nothing about the next. Do the chalk mark test again on each gun you use it with.

Wheels and studs. The calibration steps describe one test on one nut and stud. None of the documents says how worn, damaged or dirty threads change the result, so this page does not either. Check the nut and stud before you trust any setting.

The torque wrench is not perfect either. Its ±4 percent holds only inside its covered range and only while its calibration is in date. The check after a drop, and how to store it, are in the torque wrench storage guide.

Torque-limited guns are a different tool. Some air impacts limit their own output. Chicago Pneumatic's CP7748TL stops at 66 to 71 ft-lb, as covered in the same article, and its manual still says final torque goes on with a calibrated torque wrench.

On wheels, the vehicle maker's torque spec and tightening pattern come first. A stick is a way to get close faster without going past the spec, and it is not a way to reach the spec itself.

Using torque sticks the way the makers intend

1. Know the spec. Get the lug nut torque and the tightening pattern from the vehicle maker.
2. Pick the stick under it. One or two sizes below the spec, as Matco does with an 80 or 90 stick for 100 ft-lb.
3. Set up once, then hold it. Do the chalk mark test with your gun, hose, socket and pressure. Write down the air and power setting, and test again if you change any of those.
4. Keep it short. One to two seconds per nut, never past about two.
5. Finish with a torque wrench. Set it to the spec and click each nut in pattern, since that is the only step with a printed window.