What Is A Torque Wrench?


Before we get into explaining what a torque wrench is, we need to agree on what is torque…

Check out the basic terminologies and definitions here!

Thus, in other words: torque is the amount of twisting force applied to the pivot point, which is measured by multiplying moment arm length by the force applied on opposite to the pivot point end. It is very similar to the leaver and pulley systems commonly used everywhere.

Torque is not an easy to measure and estimate in common situations. That is why you need a torque wrench. In fact, the torque wrench was invented in 1918 by New York City Water Department engineer Conrad Bahr. While working on underground pipelines that carry high pressure liquid or gas, Conrad Bahr encountered an issue where for proper sealing of the pipe joints great force required to be applied, but besides large torque, for proper gasket sealing the clamping power of the nuts and bolts need to be equal. It is difficult or impossible to achieve while working in confined spaces underground or in the ditch. You can read the original patent issued for the Torque Wrench.

So what is a Torque Wrench? Torque wrench is a tool that indicates or limits the applied rotational force. Thus, according to ISO standard 6789 there are two types of torque wrenches: Type 1 Indicating, and Type 2 Setting. Type 1 has 5 classes, and Type 2 has 7 classes. This will be further discussed here.


American Society of Mechanical Engineers (ASME) maintains another classification of the Torque Wrenches. It is much more complex classification and should be left to the properly trained mechanical and manufacturing engineers. If your manufacturing facility works to ISO 9000 quality standard, the torque wrenches must be calibrated by ISO/IEC 17025 accredited laboratory. Only ISO/IEC 17025 accredited laboratory can calibrate torque wrench to internationally recognized units. In US, it is NIST, National Institute of Standards and Technology. Although most of torque wrench manufacturers claim to have calibration, only ISO/IEC 17025 accredited can give you NIST traceable calibration. It is not cheap, thus cheaper torque wrenches technically considered just “indicators”. NIST traceable calibration can cost as much as $75 for each wrench. It will definitely will not be sold for $19.99.