What is a torque wrench? How do I use a torque wrench?
A torque wrench is a tool used to tighten or loosen nuts and bolts, helping to maintain the safety and performance of equipment.
Key topics
What is torque? • Purpose of torque wrenches • How does a torque wrench work? • How to use a torque wrench? • How to adjust a torque wrench? • Does a torque wrench need to be calibrated? • What is the torque of a spark plug? • Frequently asked questions • Popular brands
A torque wrench is a tool used to tighten nuts and bolts to a predefined torque value. This tool allows fasteners to be secured with the correct tension, helping to prevent damage from overtightening or loosening from undertightening. This means that the application of accurate torque measurement is critical for equipment safety, assembly, and performance.
These tools have been used since the beginning of the 20th century; the first was developed by Conrad Bahr in 1918.
What is torque?
Torque is a measure of the magnitude of the force acting on an object, causing it to rotate, with the axis of rotation being the axis around which the object rotates. The units of torque are pound-foot (lb ft), pound-inch (lb in), or newton-meter (N m).
Purpose of torque wrenches
The torque wrench is a tool used in many industries, including home repairs, automotive, and construction. It is especially important in applications where screws and bolts must be tightly secured, as it allows the user to measure the force applied to the fasteners and ensure that it meets the recommended specifications for the job at hand.
In automotive engineering, for example, the correct torque must be maintained for all fasteners on the vehicle to ensure the safety of all persons who come into contact with the car.
Different types of torque wrenches and their uses
There are different types and sizes of torque wrenches; the main difference between them is the way they display readings and adjust them.
Electronic torque wrench
Also known as a digital torque wrench, it contains no moving parts but works with electronic sensors. It can measure the applied torque and communicate it to the user via a digital display. These tools are equipped with a small chip containing a memory stick for recording measurements; these can be later retrieved on a computer.
Beam torque wrench
This type is usually inexpensive and easy to use. It features a scale that stays on the corresponding number when the correct torque level is reached. The main bar has a handle for applying force. During use, the bar stays in place, and the scale indicates the torque level. These tools can be used for both tightening and loosening.
Click torque wrench
The click-action torque wrench is a simple and practical tool for tightening screws and bolts. It features a rotating lower part that allows the user to adjust the torque of the wrench. Once adjusted, the lower part pops out, and a clear click is heard, indicating that the desired torque has been reached.
Hydraulic torque wrench
This type is typically used in industrial environments. It utilizes the hydraulic principle to enable the conversion between torque and rotational force. The hydraulic torque wrench can easily achieve high torque values.
Micrometer torque wrench
The micrometer torque wrench is an easy-to-adjust, highly accurate tool. It is typically equipped with an adjustable torque limiter that emits a noise and/or vibration when the set maximum torque is reached. This torque wrench is widely used in fields requiring highly accurate torque control, such as aerospace and motor racing.
Pointer torque wrench
The pointer torque wrench is widely considered one of the most accurate torque measuring tools. It is wider than other types, so it can be more difficult to use in tight spaces. In addition to its widespread use in automotive manufacturing, these tools are also widely used in the aerospace and defense industries.
How does a torque wrench work?
The purpose of a torque wrench is to apply a specific amount of torque to fasteners. The amount of torque applied depends on the force applied to the handle and the length of the wrench. The following formula can be used to calculate torque: Force × Length = Torque.
Inside the handle of a torque wrench is a mechanical indicator connected to a dial. When the indicator detects that the desired torque has been reached, turning the bolt should stop. To indicate how much torque has been applied, these tools are usually equipped with an easy-to-read dial or display.
Torque wrenches can be calibrated to display different units such as pound-foot (lb ft), pound-inch (lb in) or newton-meter (N m).
How to use a torque wrench?
It's very important to use a correctly calibrated torque wrench. If it's calibrated, there's usually a label attached to the tool.
Before turning the handle, release the locking mechanism; one hand holds the pivot in position while the other grasps the handle. Then turn the tool until you hear a click. As soon as this happens, stop turning immediately, otherwise the fasteners may be overtightened.
When the tool is not in use, set the dial to the lowest value to avoid affecting the accuracy of future measurements.
Do not use a torque wrench to tighten fasteners that have already been fully tightened with a conventional wrench or socket, as these may already be tightened beyond the proper torque. Instead, loosen the fasteners and then retighten them to the proper torque.
How to use a beam torque wrench?
This type of torque wrench is primarily used for automotive maintenance and repair. First, refer to the tool manufacturer's manual for the recommended torque value for the specific type of threaded connection, then enter this value into the wrench's dial.
The dial contains a chart that shows the actual force applied to the bolt. Watch the dial carefully until the desired torque level is reached, then stop applying force to the handle.
When using this tool, you must take into account parallax error—the deviation in the pointer position due to different viewing angles. Therefore, if possible, ensure the dial is at eye level.
How to adjust a torque wrench?
By changing the tool's settings, you can increase or decrease the torque. To do this, turn the handle counterclockwise to increase the torque and clockwise to decrease it.
Does a torque wrench need to be calibrated?
To ensure that a torque wrench provides reliable and accurate measurements, it should be calibrated regularly.
How is a torque wrench calibrated?
It is recommended that all testing and measuring instruments be sent to a certified laboratory for professional calibration.
How often does it need to be calibrated?
The calibration frequency depends on the frequency of use of the tool; there are no strict or legally prescribed periods for calibration.
It is generally believed that the performance of a torque wrench will deteriorate after 2,500 to 3,000 repeated uses. Therefore, calibration is recommended after the tool has been used 2,500 times.
Even if the tool is not used frequently, it should still be calibrated once a year to ensure the accuracy of the measurements.
What is the torque of a spark plug?
When replacing automotive spark plugs, it is important to follow the instructions in the engine manufacturer's manual to determine the required torque level. Installation recommendations vary depending on the spark plug type. Below is a guide:
| Thread size | aluminum cylinder head | Cast iron cylinder head | Without torque wrench |
|---|---|---|---|
| 10mm | 8-12 lb ft | 8-12 lb ft | 1/4 turn |
| 12mm | 10-18 lb ft | 10-18 lb ft | 3/8 to 1/2 turn |
| 14mm | 18-22 lb ft | 25-30 lb ft | 1/2 to 3/4 turn |
| 18mm | 28-34 lb ft | 32-38 lb ft | 1/2 to 3/4 turn |
| 14mm cone attachment | 7-15 lb ft | 7-15 lb ft | 1/16 turn (tightened) |
| 18mm cone attachment | 15-20 lb ft | 15-20 lb ft | 1/16 turn (tightened) |
| 7/8-18 | 31-29 lb ft | 35-43 lb ft | 1/2 to 3/4 turn |
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