Set Torque vs Full-Scale Torque: What’s the Difference?

Torque is one of the most important things when you are tightening a bolt. But when you start working with torque tools, you will see terms like set torque and full-scale torque. At first, they may seem the same, but they aren’t. So, Set Torque vs Full-Scale Torque: What’s the Difference? Don’t know? Don’t worry! In this guide, I will compare both terms head-to-head. So let’s get started.

Set torque and full-scale torque both deal with torque. However, they answer different questions and serve different purposes. So what really separates them? Let’s find out the differences below.

The first difference between set and full-scale torque is what each one tells you. Set torque is basically the torque value you want to reach for a specific tightening job. For example, If a bolt is to be tightened to 50 N·m, then 50 N·m is the set torque. It gives you a clear target for when to stop tightening.

On the flip side, full-scale torque is the maximum upper limit of the torque tool’s measuring range. If a torque sensor has a full-scale torque of 100 N·m, it means it will measure torque up to 100 N·m. It does not mean you need to apply 100 N·m every time. You can still measure 30, 50, or 80 N·m with the same sensor, but no more than 100 N·m.

Full-scale and set torque also serve different purposes. For example, set torque is what controls the tightening result. You choose a certain torque value because the bolt needs that much torque. For example, if a screw has to be tightened to 40 N·m, you set the tool to 40 N·m. You can change this set torque value when you move to a different screw. This allows you to adjust the set torque to match the job.

In contrast, full-scale torque defines the torque device’s maximum measuring range. If a tool has a full-scale torque of 100 N·m, that range is the maximum. You cannot change that value by just turning a setting. If you need to measure a much higher or lower torque range than the device’s full-scale range, you will need a different measuring device.

Set torque is part of the operating range. It is the value you choose to use during the job. For example, if your bolt requires 40 N·m, you can set the tool to 40 N·m. If the next job needs 60 N·m, you can change the setting to 60 N·m. So, the set torque can move up or down depending on the nature of the work. However, full-scale torque represents the top of the measuring range. For example, if a torque sensor has a full-scale torque of 100 N·m, its specified measurement range goes up to 100 N·m. You can measure lower values, but 100 N·m is the highest value in that range.

When you tighten a bolt, your goal is not to tighten it as tight as possible. Instead, you have to create the right amount of preload. Preload is the clamping force that holds the parts or bolts together. So if we look at full-scale torque, it doesn’t tell you how tightly to tighten the bolt. It only defines the top of the torque range that the measuring device is made for. But set torque is much more handy in this regard. It helps you choose a specific torque value for the bolt. For example, if the required tightening torque is 50 N·m, you set the tool to that value and use it as your target.

Now it comes to accuracy, where set torque and full-scale torque differ. Actually, set torque gives you the target accuracy. It describes the exact torque you are trying to reach. You set the tool to 50 N·m because that is what the bolt needs. The closer the tool gets to 50 N·m, the closer you are to the required tightening value.

Once you reach 50 N·m, you have an accurate torque value for the bolt. Conversely, full-scale torque refers to the sensor’s measurement limit. Its accuracy specifications are stated as a percentage of full scale. For example, if the torque sensor has a full-scale torque of 120 N·m, it means you should not exceed that value. That’s also its safety limit and accuracy level.

When you tighten a bolt, the torque you apply creates a clamping force. That force is what pulls the connected parts together. Full-scale torque does not set the clamping force. It only tells you the highest torque value in the sensor’s specified measurement range. If the torque sensor has a torque rating of 90 N·m, you can measure 50 N·m, 30 N·m, or 40 N·m tightening operations.

However, the 90 N·m value does not mean the bolt receives 90 N·m of clamping force. In contrast, set torque is actually the operating point you choose for the tightening job. If the required torque is 50 N·m, you can set the tool to 50 N·m. If you change the set torque value, the clamping force will also change.

Different bolts and fasteners require different torque values. That’s why set torque helps you match the tightening force to the fastener. For example, if the manufacturer says a bolt should be tightened to 40 N·m, you can set the tool to 40 N·m. This prevents over-tightening or under-tightening. But full-scale torque doesn’t indicate which fastener you should use or how tightly to tighten it. It only indicates the maximum value within the sensor’s specified measuring range.

Lastly, the application range is where both torques show a clear difference. Full-scale torque is more about the type and range of work a measuring device can handle. A sensor with a full-scale torque of 100 N·m suits jobs that need torque measurements within this specified range.

If your application regularly needs 150 N·m, that 100 N·m sensor isn’t the right choice. However, a set torque is handy when you already know how much torque a particular bolt needs. You can change the value from one application to another. You can choose the set torque value that matches your tightening job. It suits many types of tightening applications.

In short: Set torque and full-scale torque are not the same values. Set torque is something you choose for the job when you need to tighten a bolt to that level. Full-scale torque is the highest value in the torque device’s measuring range. Simply put, set torque tells you what you want to use. However, full-scale torque tells you how much torque the device can measure.