How NIST’s torque tool could help keep air force jets flying

When I was young, I spent a lot of time building with Lego bricks. My room had an old, decommissioned government desk that my father bought from NIST, and I kept one of the big drawers packed full of pieces from years of Lego sets, mostly space-themed, that I built, dismantled and turned into something else. Over time, I used them to make everything from battleships that actually floated to a city filled with tunnels and bridges for my Matchbox cars. Legos were always amazing, but I never imagined those little bricks could ever have anything to do with a practical federal measurement problem.

That problem turns out to be an important one. Torque wrenches are used to tighten fasteners to exact specifications, and those fasteners matter for everything from cars to aircraft. NIST notes that millions of screws, bolts and nuts go into a single commercial jet, and each one has to be tightened just enough, not too little and not too much, to hold correctly under demanding conditions. Torque wrenches help mechanics hit that narrow zone, but the tools themselves need regular calibration to stay trustworthy.

That is where a NIST project called the Electronic NIST Torque Realizer, or ENTR, comes in. NIST says the device is a tabletop-sized, self-calibrating torque instrument that applies the same basic principle behind a Kibble balance to torque. Instead of relying on conventional mass and length artifacts the way older torque calibration methods do, ENTR uses standards of voltage and resistance traceable to the present International System of Units. That means it can be used on-site in laboratories that already have voltage and resistance standards, avoiding expensive and time-consuming offsite shipments of heavy calibration equipment.

For the Air Force, that is more than a lab curiosity. NIST says the service uses hundreds of thousands of torque wrenches that all have to be calibrated to a particular standard with a robust chain of traceability. Those tools require regular recalibration to make sure they are still measuring torque correctly. ENTR is designed to make that process faster and more practical by giving technicians a self-calibrating, highly accurate way to check torque tools on-site, saving time and money.

NIST’s measurements suggest the new device could also improve accuracy. The current ENTR version two can realize torque from one ounce of force per inch to 140-ounce-force-inches with 0.1% accuracy, and NIST says that is better than most low-range commercial torque transducers, which typically carry uncertainties of around 0.25%. Several ENTR V2 devices are now stationed at NIST and Nellis Air Force Base in Nevada, and there are plans to build even more.

Those devices can even help the Air Force improve operations and reliability. As Air Force Technical Expert for Metrology Jeremy Latsko told NIST, “This further ensures military readiness, and that doesn’t just mean the plane takes off. It means our weapon systems, and their critical subsystems, work as intended because their measurements are accurate and traceable. That means the mission is accomplished safely and effectively.”

And all this came from a few scientists who, like many of us, spent hours playing with Lego bricks in childhood. More than a decade ago, NIST researchers built a small Lego version of a Kibble balance, the ultra-precise instrument whose underlying principles would later help shape the ENTR program, out of Lego bricks. The Lego version was meant as an outreach tool and a way to demonstrate basic principles in a much smaller, more approachable form.

The Lego device was a huge success, earning a feature in the American Journal of Physics and other scientific publications. So many laboratories were interested in building Lego scales of their own that NIST created a tutorial video showing how to do it.

But the project did not stop there. In a 2022 NIST blog post, mechanical engineer Leon Chao wrote that the Lego balance “subconsciously planted a seed” for expanding the tabletop-instrument effort. That led to KIBB-g1, a first-generation tabletop Kibble balance that could directly realize gram-level masses to six digits without reference to artifact calibration weights. Chao wrote that the smaller instrument then caught the attention of colleagues working with the NIST on a Chip program, who later helped push the work toward mass and torque metrology in more compact, practical devices.

Tool manufacturer Snap-on Industrial is now part of that expansion effort too. NIST says one ENTR V2 unit is already stationed at Snap-on, and the company has been working with researchers as development moves toward ENTR V3, a larger-capacity version designed to cover a much broader torque range. In August 2024, the Air Force agreed to fund four more years of work on that next step, which NIST says is expected to measure from 0.01 to 340 newton meters with 0.5% accuracy.

The path to that next step began in an unlikely place. A pile of Lego bricks once helped make one of modern measurement science’s most exacting ideas easier to understand. Years later, that same line of thinking is helping produce a calibration tool that could make aircraft maintenance more efficient and reliable. That does not quite christen Lego bricks as military equipment. But it’s a pretty good reminder that practical federal tools sometimes grow out of places that look a lot more like curiosity than strategy.

John Breeden II is an award-winning journalist and reviewer with over 20 years of experience covering technology. He is the CEO of the Tech Writers Bureau, a group that creates technological thought leadership content for organizations of all sizes. Twitter: @LabGuys