How to Use a Torque Wrench
This easy tool tightens nuts and bolts perfectly each time
Howard Kingsnorth / Getty Images
Reviewed by Deane Biermeier
A torque wrench is a specialized tool commonly used in the automotive industry. It is made for tightening nuts, bolts, and other fasteners to a predetermined torque value, or in other words, a specific tightness. Under-tightening a nut or a bolt can lead to significant problems, like parts falling off, bending, or breaking during operation. Over-tightening a fastener presents a similar problem because you are putting the parts under too much stress during operation, which can cause the parts to warp or break. Read on to learn how to set and use a torque wrench the proper way.
What Is a Torque Wrench?
Torque wrenches are specialized socket wrench tools designed to tighten nuts and bolts to a predetermined torque value (or twisting force) to avoid accidents from under-tightening or damage from over-tightening. A torque wrench looks similar to a ratchet you'd find in a mechanics tool set, and like a ratchet, it uses sockets to drive fasteners. However, these tools are for driving only, not for loosening fasteners. A torque wrench will have a display located on the handle to indicate the torque measurement while it's in use.
When to Use a Torque Wrench
You need a torque wrench when it's critical to tighten nuts and bolts accurately without causing structural damage from over-tightening. A torque wrench must be used when assembly instructions say that a fastener requires a torque, or a specific number of pounds of pressure. Using a torque wrench ensures that the item will not fall apart when in use because the connections are tightened according to engineering specifications. A torque wrench is not required to tighten every nut or bolt, only where it really matters. For example, DIYers typically use torque wrenches for the following jobs:
Tightening a tire's lug nuts
Assembling components of trailers, car racks, and bicycles
Working on a vehicle's suspension mounting points or braking system
Repairing engine components in vehicles, including smaller engines in snowmobiles and motorcycles
Installing a lawnmower blade
Torque Wrench Types
To learn how to use a torque wrench, it's necessary to have a basic understanding of the various types and how they function.
Beam torque wrenches have a long arm or beam that attaches to the head of the tool, with a scale located near the end of the handle. When the torque wrench beam flexes, the scale indicates the amount of torque currently being applied. Tighten the fitting until the scale meets the intended torque level for the project.
Split beam torque wrenches work in the same way as beam torque wrenches. Split beam torque wrenches have a secondary beam that runs behind the main arm of the tool, which flexes to indicate the torque on the scale, instead of the main arm bending. This change in design improves the life and overall durability of the wrench compared to a standard beam torque wrench.
Click torque wrenches are the most common with DIYers and professionals. You need to set the desired torque level by twisting the base of the wrench to line up with the intended setting listed on the handle. Once the torque level is set, you can position the wrench on the fastener and begin tightening until you hear an audible click.
Digital torque wrenches are made for convenience and accuracy. Similar to the click torque wrenches, you will need to set the desired torque before you can start to work. This style of torque wrench is the most expensive option, and it requires batteries to run, though the precise measurements and easy-to-read digital screen may make the added expense worth the investment.
Warning
A torque wrench is only designed for tightening fasteners and should never be used to loosen a fastener. This can damage the wrench or impact the calibration of the wrench. This is not an adjustable wrench, however, you can adjust the torque value on click and digital versions.
How to Use a Torque Wrench
Set the Torque Level
Set your torque wrench in pounds by using the digital screen or the markings on a click torque wrench. For example, if the torque specifications for your project require 40 pounds per square inch (or 40 inch-pounds), set the wrench to 40.
Click Torque Wrench
To set the torque value on a click wrench, you need to twist the base of the wrench so that it lines up with the desired torque level (typically foot-pounds, inch-pounds, and/or Newton Meters) imprinted on the handle. Read the wrench's instructions to know what all of the markings on the handle mean and how to correctly rotate the base to the right torque level.
Digital Torque Wrench
To set the torque value on a digital torque wrench, use the digital controls to increase or decrease the torque value. Press the set button to verify your selection.
Position the Torque Wrench on the Fastener
Tighten the nuts and bolts by hand until they are snug before using the torque wrench.
Make sure you have the right size wrench for the job. Wrenches that accept 1/2-inch and 3/8-inch sockets are the most common sizes for automotive work, though a 1/4-inch torque wrench may be better if you are working on a bicycle.
Choose the appropriate size socket and secure it to the wrench. Line up the torque wrench with the fastener and slide the head onto the nut or bolt. Apply a small amount of pressure to test the fit of the torque wrench. If you feel the wrench slipping on the fastener, consider trying a smaller socket to avoid stripping the fitting.
Tighten the Fastener
Turn the torque wrench slowly to tighten the fastener and continue turning until you have reached the target torque level.
Click Torque Wrench
If you are using a click torque wrench, you'll hear a click when it's tight. Keep in mind that the click does not disengage the wrench, so if you don't hear it or choose to ignore it, you can end up over-tightening the fitting.
Digital Torque Wrench
While some digital torque wrenches have programmable tolerance limits, this isn't a standard feature. Instead, you need to rely on a buzzer or light to indicate when you should stop applying torque.
Tip
Beam and split-beam torque wrenches cannot be pre-set to a specific torque level, so they do not have auditory or visual prompts to indicate when you have reached the target level.
Keep an Eye on the Torque Reading
Until you reach the appropriate torque level, it's recommended to regularly check the current torque applied to the fitting. With a beam or split beam torque wrench, this is mandatory because you do not have any other way of determining when you have reached the target torque level.
Click and digital torque wrenches have auditory or visual signals that indicate when to stop applying force to the wrench, but if you accidentally set the torque wrong, or you missed the signal to stop, then you can end up under-tightening or over-tightening the fastener.
When you hear or see the signal, immediately release the torque wrench to avoid over-tightening.
Check the physical scale on a click-style torque wrench or use the digital screen on a digital torque wrench to make sure you don't exceed the recommended torque level.
Tips for Using a Torque Wrench
Using and caring for a torque wrench is a bit more tricky than many other tools and types of wrenches.
Do not exceed the maximum torque limit of your wrench. If assembly instructions require a torque your wrench cannot handle, you may need an additional torque wrench to finish the project.
When using a torque wrench, it's important to hold the handle of the wrench correctly. There may be a mark on the handle indicating where to hold it. If not, place one hand on the head of the wrench to make sure the rotation occurs and your other hand should be on the handle to apply the force. Holding the torque wrench wrong may result in an inaccurate torque value.
Clean the fastener's threads. Only lubricate threads if assembly instructions say it's necessary.
Practice setting up and using a torque wrench before your project to get used to the feeling and sounds of the wrench.
Store your torque wrench in a protective case so it is not jostled or dropped.
When to Replace Your Torque Wrench
Torque wrenches are intended to display accurate torque readings, but they require regular calibration to remain accurate. You should calibrate your torque wrench or have it professionally calibrated at a tool repair service about once every year, but keep in mind that torque wrenches do wear out over time, generally after about 100,000 tightening cycles. Wrenches can also become warped and weakened from repeated attempts to bend the arm back into proper alignment. If this occurs, it's recommended to replace the torque wrench. To extend the life of the tool, avoid dropping the wrench and don't allow it to sit for a long time without use.
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