Torque Wrench Accuracy

I have an old click type torque wrench. When there is a torque range given for a bolt or nut, I shoot for a value in the middle, assuming there is some inaccuracy in my wrench. But I have no idea of how inaccurate my wrench is. Is there any way to know?

I guess you could hang a lead weight from it, set it at the expected value and see if it clicks?
ie, 5lb weight at 1ft" should click at 5Lb/Ft, if the wrench goes that low.

I look at the torque wrench as a way to (hopefully) have bolts equally torqued.

Interesting thought above by James…

I think you could do some testing in a similar manner to how people compare tire pressure gauges. Use a few different wrenches, see where most of them trend. If yours is the outlier…well…

It depends on the manufacturer and the use since the last calibration. The accuracy also usually varies through out the range of the wrench but I think clickers usually have a 4-6% accuracy (when new).

Use them a lot, or leave them lying around set at the highest torque level and that inaccuracy will increase. Trick is to keep it calibrated.

Often there are torque wrench calibration services that visit shops with calibrate wrenches in the back of a truck.

In terms of checking accuracy, get a torque wrench you know to be accurate (recently calibrated), set it the same as the torque wrench you are checking. Tighten a bolt you know isn’t going to stretch to the set torque with the known torque wrench, mark it with a paint pen so you know its position. Undo it and tighten it with the unknown torque wrench, they should click near the same place and the paint pen mark should line up.

Otherwise go to a calibrator and get it recalibrated.

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So then maybe the best bet is to talk to a local mechanic and see who they use to calibrate their wrenches?

Or a machine shop, they will at least be able to point you in the right direction.

I had one go out of calibration from leaving it at the setting while stored. Didnt realize it until i had repeated engine failures from coolant getting into the combustion chamber. I use an inline tranducer one now and use a standard ratchet. Its never in the stressed state unless it’s being used so its less susceptible to the creep assosciated with the spring in a standard click style torque wrench. Something like this:

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Most tool trucks have torque wrench testers in them now days. If it needs calibrated they would still have to send it off but it would give you an idea.


Thank you everyone for the responses. Haven’t seen a tool truck in the neighborhood lately but I’ll an eye out for one. Paolo, that’s an interesting tool and will think on that. We have been good over the years about zeroing out the wrench after each use but its been used for many years. Thanks.

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You can pretty much spend as much as you want to spend on torque wrenches. The engine assembly plant I was the process engineer for a couple of years had $10k transducerized torque wrenches for each critical fastening.

Those sorts of torq adapters are great but it is just another thing to get calibrated.

10K is a little over my budget. The only thing I work on now-a-days that needs a torque wrench is kart related. I’d like to be sure that when I torque a head bolt to 180 inch/pounds it’s close.