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How to calculate the metric bolt torque

Updated March 28, 2017

Torque ratings are important when using bolts or other fasteners to prevent overtightening or compromising the integrity of the metal. The metric system, used in most countries around the globe, is a system of measurements based on increments of 10. Most bolts gain torque measurements based on the metric system of measurements. To get a proper metric torque measurement for a bolt, gather information about the bolts in question.

Zero out the calipers, either by sliding an old-style caliper into the zero position or by pressing the reset button on new electronic versions. Place the calipers over the round non-threaded portion of the screw. Take the measurement, in metric, and write it down. This is the bolt's major diameter.

Determine the metal used to make the bolt; examples include brass, steel or aluminium. Write down the material.

Hold the metric ruler up to the threaded section of the bolt and measure from the bottom of the bolt to the top of the threads. Write this measurement down in millimetres. This is the thread length measurement.

Write down any miscellaneous information you may have about the bolt, such as tensile strength.

Enter these measurements into a bolt torque calculator. Calculators are available online for free, or you can opt to download software for a torque calculator. Many of these programs are free. Wait for your metric bolt torque rating to appear on the calculator.

Things You'll Need

  • Metric calipers
  • Torque calculator
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About the Author

A former Alaskan of 20 years, Eric Cedric now resides in California. He's published in "Outside" and "Backpacker" and has written a book on life in small-town Alaska, "North by Southeast." Cedric was a professional mountain guide and backcountry expedition leader for 18 years. He worked in Russia, Iceland, Greece, Turkey and Belize. Cedric attended Syracuse University and is a private pilot.