What is 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.
Why Do You Need a Torque Wrench?
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.
Types of Torque Wrenches
So how does a torque wrench work? To answer this question, you first need to understand the different types. The three primary types of torque wrenches are click, digital and beam models. While they all allow you to drive a fastener to a specific torque, they each function differently, and some are easier to use than others. We've got general steps below for using each type to drive a fastener to different torque values, but fastening jobs and tool models differ. Always use torque specifications for your work and follow the calibration, setup and use instructions for your wrench.
How to Use a Click Torque Wrench
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.
