What is the best way to perform a torque wrench calibration?

By: HowStuffWorks.com Contributors  | 
Three torque wrenches lying on a workbench.
Torque wrenches are a commonly used across a wide variety of industries. Shutterstock: Thusbaudin PH

A torque wrench is a tool that measures the tension, or twist, of bolts and nuts to make sure they’re tight enough without over-tightening them. The key to their usefulness is proper torque wrench calibration. Read on to learn more about these irreplaceable precisions tools.


What Are Torque Wrenches?

Used in a variety of industries including automotive, manufacturing, and aerospace, torque wrenches are precision tools designed to apply a specific torque to a fastener such as a nut or a bolt.

By measuring the correct degree of tensions applied to a fastener, torque wrenches effectively prevent under- or over-tightening, as well as all of the mechanical or safety issues that can arise from an improperly tightened fastener.


They come in a variety of types, including:

  • Click type torque wrenches: By far the most popular variety. This variety of torque wrench clicks to notify the user that the correct torque has been applied [source: Keebler].
  • Beam type torque wrenches: Not nearly as precise as some of the other types, beam type wrenches rely on an indicator bar that bends when torque is applied.
  • Digital torque wrenches: Outfitted with a digital screen, these wrenches are ideal in situations that require exact torque specifications.
  • Hydraulic torque wrenches: These industrial tools use hydraulic power to apply large amounts of torque with pinpoint accuracy.


Why You Need a Torque Wrench

A torque wrench is not like the other tools in your tool box. Whether you're a professional engineer or an at-home DIYer, the ability to generate reliable torque readings is essential to ensuring the mechanical integrity and safety whatever it is you're working on [source: Dale]. Broadly speaking, adding a torque wrench to your toolbox will help:

  • Guarantee precision and accuracy
  • Prevent over tightening
  • Avoid under-tightening
  • Ensure safety
  • Ensure peace of mind
  • Avoid undue damage and maintenance costs.

You don't have to be a professional mechanic to benefit from a properly calibrated torque wrench. So, make some space in your tool box and be amazed at how often you find yourself using it around the house.


How to Calibrate a Torque Wrench

Proper calibration is key to a torque wrenches usefulness. Torque tools are designed for accuracy and reliability, and they can't deliver on either of those promises without calibration. Though the process is a little complex, you can calibrate a torque wrench at home with the following steps:

  • Gather and set-up required equipment: To calibrate a torque wrench yourself, you'll need to invest in a calibrated torque tester, which is a device specifically designed for torque testing. Be sure to set it up in accordance with the manufacturer's instructions.
  • Prepare the wrench: Set the torque wrench to its lowest setting and gradually increase to the desired calibration point.
  • Apply torque: Attache the wrench to the tester and apply force steadily and evenly.
  • Read the measurements and adjust if necessary: As you apply torque, read the measurements and adjust the wrench by turning the adjustment screw on the torque tool.

Though they can come in handy, know that you don't have to invest in heavy duty torque testers to guarantee the accuracy of your torque tool.


To calibrate your wrench without a torque tester, you need to determine the calibration ratio and multiply that amount by the required bolt torque. The torque wrench has the option of measuring distance in inch pounds or foot pounds [source: Manouchekian].

First, measure the distance from the center point on the wrench head to the point at which you apply the most pressure on the wrench. Then clamp the wrench bit in a bench vice and hang a 20-pound (9-kilogram) weight from the handle of the wrench with a string. Move the string until it measures 40 foot pounds (or 480 inch pounds.)

Next, measure the distance from the center point on the head of the wrench to the string. Divide the second distance by the first to find the calibration ratio. Finally, set the torque wrench to the product of the calibration ratio and the required bolt torque.

While DIY calibration is possible, for high-precision applications or if you're unsure about the process, it's best to enlist the help of professional torque wrench calibration services.


Precision, Safety, and Accuracy

From ensuring the safety of vehicles on the road to maintaining the integrity of critical machinery, the torque wrench plays a pivotal role. Through understanding what they are, recognizing their importance, learning about their calibration, and acknowledging the necessity of having one, we gain a deeper appreciation for this essential instrument.

The journey through the types and functionalities of torque wrenches reveals a tool not just for tightening bolts but for safeguarding the reliability and safety of mechanical systems. Whether you're a professional mechanic, an aerospace engineer, a DIY enthusiast, or someone who takes pride in doing the job right, a torque wrench is your ally in precision and excellence.