Revised Torque Wrench Tips
May 30, 2018
In the past I've offered tips on how to correctly use torque wrenches. Having recently talked with torque wrench experts at Mac Tools and Snap-on Tools, here are a few additional things I've learned.
First, it's okay to use a short (2" to 4") socket extension on a torque wrench. It's technically okay to use a longer extension, but the engineers were concerned that with a longer extension there is risk that the length of the extension will "load up" and absorb some of the torque, like a torque arm on a vehicle suspension. If the extension "wraps up" with torque just before the target torque is reached, some of the torque might be temporarily "stored" in the extension so that the torque wrench doesn't click or register that target torque has been achieved. That's a tough one to explain, but when you think about it, it makes sense. The shorter, 2" to 4" extensions are short enough so they shouldn't "load up" with torque.
The other concept the engineers emphasized was that crowfoot wrenches, or torque adapters (aka, "dogbone wrenches), shouldn't be used with a torque wrench. A torque wrench is designed to measure torque from the center of its head (directly over the nut or bolt being torqued) to the center of the handgrip. Anything that changes the distance between the center of the fastener to the center of the handgrip distorts the torque reading.
A final concept the engineers emphasized was that a torque wrench should never be used to break loose nuts or bolts. The sudden release when a fastener breaks loose can knock the torque wrench out of calibration. Use a power wrench or breaker bar to loosen and remove fasteners.
And, for those of you who use a torque wrench frequently, the American Society of Mechanical Engineers (ASME) recommends checking the calibration of torque wrenches every 5,000 uses/clicks/"beeps) or once a year, whichever comes first.