How to Use a Torque Wrench

In terms of fasteners, torque relates to how tightly a fastener is secured. A torque wrench is the tool you use to drive a nut or bolt to a specific torque. In many fastening applications, this is necessary:

• For Safety: Fasteners that aren’t tightened sufficiently, such as a nut on a bike wheel, can loosen due to moving parts or vibration. Fasteners that are too tight risk breaking the fastener so it no longer secures the parts.
  

• To Prevent Damage: Tightening fasteners too much, such as overtightening the lug nuts on a vehicle wheel, can damage the fasteners and the components they’re securing.

• To Set a Series of Fasteners to the Same Torque: In some applications, such as attaching a cylinder head to an engine, it’s critical that all fasteners are driven to the same tightness.

A torque wrench looks similar to a ratchet you’d find in a mechanics tool set and, like a ratchet, uses sockets to drive fasteners. However, these tools are for driving only, not for loosening fasteners. Torque wrenches have different drive sizes ranging from 1/4 inch to 1 inch to fit different size sockets. In general, wrenches with smaller drive sizes are for work on small equipment, such as bikes or small engines, and applications that require less torque. Larger sizes are for more heavy-duty work, such as installing lug nuts on a wheel or working on construction, farm and commercial trucking equipment. For do-it-yourself projects, a 3/4-inch or 1/2-inch drive will handle most of your jobs and fit sockets that work on most of the fasteners you’ll need. Need tips on finding the right sockets for your project? See our ratchet and socket guide.

In addition to the drive size, a torque wrench will have minimum and maximum torque settings, measured in inch-pounds (in-lbs), foot-pounds (ft-lbs), newton-meters (Nm) or meter-kilograms (mkg). The tool manual should provide a chart to allow you to convert different measurements, such as converting newton-meters to foot-pounds.

You need a torque wrench for any project that requires precise tightening. If assembly instructions indicate a specific torque, don’t try to use a wrench or ratchet. You need a torque wrench. Automotive repairs and maintenance — like tightening lug nuts on a wheel, rebuilding an engine or assembling a brake system — are some common applications for a torque wrench. Other uses include assembling a bicycle, installing a mower blade, working on a trailer or assembling a vehicle storage rack. Different fastening jobs have different specifications; you may need torque wrenches with different torque ranges. Don’t try to make a wrench work beyond its capabilities.

So how do you set a torque wrench? On a click torque wrench, the handle is imprinted with horizontal lines at major gradations of torque — such as 100, 110, 120 or 130 foot-pounds — and a vertical index mark. A rotating portion of the handle is marked with vertical index marks at minor gradations of torque: 0, 1, 2, 3, etc. Once you’ve tightened a fastener to the designated torque, the wrench produces a click that you can hear and feel through the handle. Setting a click torque wrench up properly may seem a bit complex at first, but the click feature makes it easy to determine when you’ve reached the correct tightness. It also makes this model a good option for work in situations when you can’t read a gauge or display or where you may not be able to hear an audible signal.

A digital torque wrench, also known as an electronic torque wrench, allows you to easily program the desired torque using buttons and a display screen. Like a click model, the wrench emits an audible signal when you tighten a fastener to the desired torque. In addition, the screen shows the torque measurement, and some models display an indicator light and vibrate. These models make it easy to know when you’ve tightened a fastener properly, even if you can’t see the screen or hear the audible alert. Digital torque wrenches are also good for smaller foot-pound tightening as they’re more precise. Some models allow you to use different units of measurement to fit your application, and some alert you when you get close to the desired torque value, reducing the risk of accidentally overtightening a fastener.

A beam torque wrench uses a simple pointer and scale to display torque. It usually won’t require setup; the scale simply moves under the pointer as you apply force to the handle. It’s relatively simple to use, and you can often recalibrate it yourself. However, viewing the reading can be difficult, depending on the orientation of the wrench. And, since you’re relying on a visual indicator rather than a click or beep, you’ll need to ensure you’re reading it accurately.

A torque wrench is a delicate piece of equipment. Torque wrenches require careful handling and need proper maintenance to function accurately. Mishandling can damage the tool or disrupt the calibration, meaning your fasteners won’t be torqued correctly. Your manual will have full instructions, but here are some tips for using and taking care of a torque wrench:

• Handle the wrench carefully. Avoid bumping or dropping it.
  
• Be aware of the maximum torque limit of the wrench and never exceed it. If you need to torque a fastener beyond the tool’s limit, you need an additional torque wrench.
• Make sure the fastener threads are clean. In most cases, you’ll apply fasteners without lubricant. Lubricate the fastener threads only if instructed to do so.
• Use a standard wrench or ratchet and socket to loosen fasteners. Never use a torque wrench to loosen fasteners. For stuck fasteners, use a breaker bar.
• Grip the handle correctly when tightening a fastener. The handle may be marked to indicate where you should hold it. Holding the handle too close or too far from the fastener will reduce accuracy of the torque value.
• Never use a handle extension. In some cases, you may be able to use a drive extension, but it’ll change the torque output. Check your manual for the procedure to correctly calculate the torque with a drive extension.
• Get the wrench recalibrated regularly. With a beam model, you may be able to calibrate the device yourself. Other types require professional servicing.
• Wipe the wrench clean and set it to the lowest torque setting after using it.
• Keep the wrench in its case and store it in a safe location when it’s not in use. Most models come with a protective storage case.