Torque wrenches are specialized socket wrench tools that are common in the automotive industry. They are 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.
Torque wrenches can also be used on bicycles, lawnmowers, and other small engines, like snowmobiles or motorcycles.
What Is a Torque Wrench?
Torque wrenches are specialty tools designed to tighten nuts and bolts to a predetermined torque value, avoiding accidents from under tightening or damage from over tightening.
Torque Wrench Types
In order 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.
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.
How to Use a Torque Wrench
Set the Torque Level
If you are using a digital or click torque wrench, set the target torque value. Use the digital controls to increase or decrease the torque value, then press the set button to verify your selection.
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 listed on the handle.
Position the Torque Wrench on the Fastener
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 to tighten the fastener and continue turning until you have reached the target torque level. 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.
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.
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.
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.
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 about once every year, but keep in mind that torque wrenches do wear out over time. 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 period of time without use.