Rethinking Industrial Fastening: why tension matters more than torque
At TRAXX, we’ve made it our mission to address this issue head-on by focusing on what truly matters: measuring and controlling BOLT TENSION.
🔩 The Problem with Traditional Torque-Based Tightening
For decades, most bolted joints have been assembled using torque tightening — applying a predefined amount of torque, based on the assumption that it directly correlates with the tension inside the bolt.
That assumption is not only flawed — it’s dangerously imprecise.
According to Michel Berbesson, Technical Director at TRAXX, field data shows that torque-based methods can result in tension variations of ±50%, even when using calibrated tools and skilled operators.
Why? Because 80% of the torque is lost to friction, and only 20% contributes to actual bolt stretch.
And friction is unpredictable — it varies with lubrication, surface finish, temperature, humidity, corrosion, and more.
A small change in friction can dramatically shift the amount of tension, without any indication to the operator.
📐 Precision Cannot Be Assumed — It Must Be Measured
Even the most advanced torque wrenches in the world can’t guarantee consistent tension.
When bolts are too tight, you risk thread damage or shearing. When they’re too loose, joints can loosen or fail entirely.
Industries like aerospace, automotive, energy, and nuclear power — where safety is non-negotiable — can no longer afford to rely on guesswork.
🛠 What Actually Holds a Bolted Joint Together?
The key to joint integrity isn’t torque — it’s tension.
Tension is the axial force created when a bolt is stretched. This clamping force presses the assembled components together and keeps them from separating during use.
It is this internal force — measured in newtons (N) or kilonewtons (kN) — that defines whether a joint will hold or fail.
Yet, most operators don’t have access to tension measurement tools during assembly.
Instead, engineers provide torque targets calculated from CAD simulations and theoretical tables — because torque is the only variable they can easily control.
But controlling torque doesn’t mean controlling tension. And that’s the heart of the issue.
🔧 The TRAXX Approach: Measure What Matters
Fortunately, there’s a proven and precise alternative:
Ultrasonic tension measurement.
When a bolt is tightened, it elongates slightly. By sending an ultrasonic pulse through the bolt and measuring its travel time (time of flight), it’s possible to determine the change in length — and therefore the actual bolt tension.
This technique, though known since the 1970s, was once unreliable due to poor electronics.
Today, with high-performance systems like TRAXX-M2, this method is now fast, accurate, and non-intrusive.
🔄 But Can You Measure Tension After Tightening?
This is the question we hear most. And the honest answer is:
❌ No, you cannot measure the tension of an already-tightened bolt unless you recorded its initial condition.
Even so-called “absolute” methods tested over the past 40 years have proven too inconsistent to be reliable.
Empirical alternatives, such as breakaway torque tests, are often misleading — a rusted bolt may require huge torque to loosen, even though the tension is zero.
TRAXX-M2: Reliable Tension, From Day One
That’s why the only reliable solution is to measure tension from the beginning.
TRAXX developed the M2 system, a “plug & play” ultrasonic tension meter designed to deliver real-time, high-precision measurements of bolt load.
With TRAXX-M2, you can:
🔩 Tighten bolts directly to their specified tension during assembly — fast, accurate, and repeatable.
🔍 Check existing tension at any time, without disassembling the joint (measurement takes just seconds).
📈 Monitor tension changes in real-time during machine operation — ideal for predictive maintenance.
Already in use by leading manufacturers in aerospace, nuclear energy, and transportation, TRAXX-M2 sets a new standard for bolted joint control.
Conclusion: From Torque to Tension
Torque-based tightening is a legacy method.
Modern industry demands higher performance, tighter control, and fewer failures.
And that begins by measuring what really matters:
Tension.
TRAXX helps manufacturers shift from assumptions to certainty — one bolt at a time.
Want to learn more about ultrasonic tension measurement?
Reach out to our team of experts.