There are two basic laws in the world: gravity and entropy. Gravity makes things fall down and is the reason the aerospace industry exists. Entropy makes things fall apart and is the reason you have to clean things after you’ve just cleaned them, adjust settings you’ve just adjusted, and may not feel as young as you used to.


In the world of manufacturing, entropy is the reason why your equipment, specifically your torque control tools, slip out of alignment and require recalibration. Simply put, the more you use a torque wrench, the more likely it is to need calibration. To help you combat the entropic forces slowly wreaking havoc on your torque equipment, we’ve put together a guide to everything you need to know about the >calibration of your torque equipment according to ISO standards.

The Importance of Proper Torque Calibration

>First, what are we talking about when we talk about calibration? Calibration is the process of ensuring that the workings of your instrument correspond to their posted standards. For example, if your car’s speedometer is properly calibrated, then when the car travels 50 mph, the speedometer displays “50 mph.” If the speedometer is not properly calibrated, then when your car travels 50 mph, your speedometer may read “55 mph,” or “35 mph,” or “100 mph.” As you can see, achieving and maintaining proper calibration is essential to the safe and effective operation of your equipment.

>As applied to torque tools, calibration means that the tools accurately register the torque they are applying to a given fastener. Considering the purpose of torque tools is to deliver a precise amount of radial force to a fastener such as a bolt or screw, if they are out of calibration, they will not be able to perform their function. If a torque tool registers that it has delivered more torque than it actually has, the fastener may become over-tightened, causing it to deform or break when your product is in use. On the other hand, if your torque tool registers that it has delivered less torque than it actually has, your fastener may not be tight enough. As a result, it could back off and come loose while your product is in operation. Fasteners aren’t given torque specifications for no reason—if a bolt comes loose or breaks, it can have dangerous repercussions for the product and anyone near it. For this reason, it’s essential to know that when your torque wrench says it has delivered 8.4 ft.lbs of torque, it has delivered exactly that, no more and no less.

>With this in mind, the next question is, “What do I need to do to keep my torque tools in calibration?” Fortunately, keeping torque tools calibrated is not an onerous task. There are only two steps involved, in fact: test the calibration of your wrenches and recalibrate wrenches which have fallen out of alignment.

ISO Torque Wrench Calibration Standards

The current international standards governing the calibration of torque wrenches are the ISO 6789-1:2017 and 6789-2:2017. The two standards are published by the same body, the International Standards Organization, and they are interlinked. While the first part is concerned with design and quality conformance testing and the second focuses on measurement uncertainty and calibration requirements, essentially, they are two parts of the same whole. According to these guidelines, torque tools should be tested for calibration once every 5,000 cycles or six months, whichever comes first. If any tool is found to be out of calibration, it must be recalibrated, retested, and recertified. To ensure it does not slip out of calibration again without being noticed, the calibration interval for that particular tool is then halved to 2,500 cycles or three months.


Testing your torque tools can be accomplished by a variety of means. The simplest is to send them to a certified laboratory. Laboratories in the United States will be certified by the National Institute of Standards and Technology (NIST). This is separate from the ISO, which is an international body and limits its responsibility to the publication of standards, not their verification or enforcement. NIST, by contrast, is a branch of the U.S. Department of Commerce.

This is a typical arrangement; while the ISO itself does not enforce its guidelines, many governmental bodies, such as the Federal Aviation Administration and the Food and Drug Administration, have enshrined ISO standards into their codes of regulations. Even if your particular product does not require conformity to ISO standards under applicable bodies of law, ISO compliance remains a gold standard for quality workmanship and safety. Companies which comply with ISO guidelines, therefore, will have a competitive advantage over companies which don’t. As an added bonus, companies in compliance with ISO standards will also be better protected from accidents and repercussions due to shoddy workmanship.

Methods of Establishing Torque Tool Calibration Regimens

Laboratories certified under NIST standards will test your tools using approved methods, recalibrate them if necessary, and provide you with complete paperwork according to standard to certify their work, whether or not the tool was found to be out of calibration. The primary benefit of sending your torque tools to an outside laboratory is simplicity—your torque calibration regimen is as easily accomplished as pulling tools from the line and putting them in the mail. Among other benefits, this method is also reliable and will allow you to rest assured that your torque tools have been handled by trained, experienced professionals.

However, sending your torque tools into a laboratory does come with some drawbacks. For one, the service will cost your company, requiring you to dedicate a portion of your budget to calibration assurance. Plus, you will have to wait for shipping on both ends, in addition to the time it takes to test and recalibrate, before returning your tools to service. Finally, each time you send in a tool, you’ll have to fill out paperwork. While that paperwork won’t be onerous for any single tool, if you’re sending in dozens or hundreds of tools for calibration, the aggregate paperwork will require a certain time investment. Some laboratories, such as Mountz Inc.’s, streamline this process by allowing blanket purchase orders to cover a predetermined number of tools or service budget.

Nevertheless, some companies choose to develop their own torque testing and calibration protocols. The most basic level of in-house torque calibration is establishing a testing regimen and only shipping tools in for service if they need calibration or are otherwise broken. The advantage of this method is a reduction in shipping costs and the amount of time that tools are out of service. Establishing a torque testing regimen is as simple as purchasing the correct equipment, such as a torque analyzer for hand tools and run-down adaptors and analyzers for power tools, then training personnel in their use and establishing a testing regimen. Of course, these testing devices are only as good as their calibration, so they themselves must be tested at regular intervals to ensure they retain their accuracy. This can be accomplished in-house with trained personnel and standard calibration equipment, or your torque testers can be shipped to a certified laboratory for calibration and service.


Finally, some companies prefer to do it all themselves. For the most part, these companies employ torque tools on a sufficient scale to justify the cost of establishing their own torque laboratory with the amount of time and money they save by performing testing and calibration in-house. In addition to torque testers, they must also invest in torque calibration equipment. This includes a set of standard deadweights, a segment, or a calibration wheel, which represent the official equipment by which torque testers and sensors are calibrated and can be traced to National or International Standards such as N.I.S.T. and ISO.  In addition, you can use loading benches to hold your tools if you are dealing with torque wrenches specifically. While entropy will have an effect on deadweight, it takes a very, very long time, rendering these acceptable means of applying a specific amount of force to torque tools for testing purposes. Finally, if in the United States and seeking accreditation (which most businesses at this level are), your torque testing regimen must be inspected and certified by the NIST to ensure it is in compliance with ISO standards.

While this may seem like a large number of requirements, it still boils down to two basic requirements: test your tools and recalibrate your tools as needed. Deciding if it makes more sense to send your tools to a third-party laboratory for testing, calibration, or both depends on the number of tools you’re using and the needs of your business. Often, as is the case with Mountz, the company which sold you your torque tools in the first place will have laboratories where you can test them. Whether you send your tools to the original equipment manufacturer or not, be sure that the laboratory you employ is certified under NIST standards. Happy calibrating!

At Mountz Inc., we understand that tools aren’t built to be used only once. That’s why we put so much effort into ensuring our tools are as durable and long-lasting as possible. That’s also why we staff two full, certified calibration laboratories, in Foley, Alabama and San Jose, California. For more information about our calibration services or our high-quality torque tools, contact us today.