The Quarter-turn Solution
WHEN THE SPACE SHUTTLE CHAL - lenger was destroyed in 1986 by the failure of an O-ring, it tragically brought home the familiar technological truth that the breakdown of a seemingly insignificant part can trigger an enormous catastrophe. A complex system like the space shuttle contains hundreds of components and subsystems that can go wrong, and the seals and connections between them greatly multiply the potential for failure. The fundamental lesson has never been more succinctly summarized than by the renowned racecar engineer Carroll Smith in his Nuts, Bolts, Fasteners and Plumbing Handbook : “The price of joining elements into structures is the occasional structural failure. The joint is always the weakest link in the structural chain. The fastener is always the weakest link in the joint.”
Educated early in this inescapable fact of technological life, engineers learn (or should, at any rate) to pay close attention to fasteners in the structures they design. The rest of us come to appreciate the importance of fasteners in other ways, all too often when one of them fails. On August 24, 1970, about nine miles into my second practice lap for motorcycling’s Manx Grand Prix on the Isle of Man Tourist Trophy course, I began to develop an appreciation for William Dzus and the fastener he invented in 1931—because his fastener didn’t fail.
Like most of the people who used Dzus fasteners in aviation and motor sports—mechanics, racers, pilots, design engineers— all I really knew about Dzus’s invention before that day was what it was for, how to use it, and how to pronounce it (“Zeus“). I knew it wasn’t a structural fastener, since its purpose was to join together nonstructural panels in a way that would allow quick assembly and disassembly. I also knew that to use the Dzus, you needed only to push the slotted male stud (usually held in place on the outer panel by a clip on its shank under the panel) down into the receptacle on the lower panel, so that the stud’s slotted shaft drops over a transversely mounted piece of piano wire. Since the stud has a spiral slot cut circumferentially into its shank, turning the stud engages the wire so that it rides up what is, in effect, a cam-shaped ramp, until it snaps into a detent at the end of the slot. The two panels are thus held together by the spring tension of the piano wire, providing a joint that was both secure enough for the aerodynamics of fuselage or body panels and quick to lock and unlock—which was why, at the Manx GP, six Dzus fasteners clamped the “belly pan” of my 348cc Shepherd Kawasaki’s streamlining to the main body of the fairing. This application of the Dzus was typical: It was used where trying to get a wrench on a nut inside the inner fairing panel—next to the red-hot exhaust pipes—would have been too time-consuming and uncomfortable, since “buttoning up” the fairing was usually done in the last, frantic moments before wheeling the machine to the starting grid.
But I was thinking about the TT Mountain Course, not fasteners, as I accelerated the bike through the left-hand turn just before the Laurel Bank right-hander. The 37.75-mile course is lined with so many hazards—stone walls, fences, cliffs, trees, curbstones—that a racer’s memory is crucial to survival. And though this was only my second practice lap, as I dove into the turn before Laurel Bank, I was sure I recalled the right line to get through it safely and quickly.
I was wrong. I arrived at the entrance to the right-hander going much too fast. Even so, I tried to make it through, leaning the bike over until the right side of the fairing dragged on the pavement. But I leaned too far, and as the tires lost their grip, the Kawasaki fell, flipped, and spat me off. It skated on its side up against the wall of the bridge, where, a heartbeat later, I slid to a stop next to it.
As I examined the battered bike, I realized that while all three of the pan-head machine screws that clamped the fairing tightly to mounting brackets had been sheared in the crash, the Dzuses had remained locked, keeping the belly pan in place. The panel fasteners had not been subject to the same stresses as the machine screws, of course, but I was nonetheless impressed, and I began to think seriously about fasteners for the first time. As I continued to race and test motorcycles and automobiles, and then to fly light aircraft, the Dzus fascinated me, partly because of its interesting design—combining the simple and the complex—but mostly because no Dzus on any of my vehicles ever failed, in spite of extreme operating conditions and incidents even more dramatic than my accident at Laurel Bank.
In his book Carroll Smith says that “Dzuses tend to be easier to find, more forgiving of minor misalignment and more positive in their locking action” than other types of quarter-turn fasteners. This praise from a famous engineer would have gratified William Dzus, who was born a Ukrainian peasant in 1895 and died a wealthy American industrialist in 1964. For Dzus was both an inventor and a machinist-craftsman deeply imbued with the skills and values of the machine shop. Early in his life he showed the traits that would be critical to his later success. When he wanted a bicycle at age seventeen, for example, being too poor to buy one, he simply made one—entirely from wood, with rope for tires.
As Dzus’s biographer, Ronald Lawrence Bern, tells the story, Dzus’s father destroyed the wooden bicycle in a rage, presumably because it showed that William was wasting his energy on something other than farming. The little village of Czernychiwci thereupon ceased to be big enough for William, who detested farm life. He wangled twenty-five dollars and a one-way ticket from a great-uncle and made his way to Montreal, where a Dzus uncle lived. From there William could get a visa for entry into the United States.
When he boarded the ship in Bremen, the eighteen-year-old Dzus had a thin résumé: eighteen months as a carpenter’s apprentice, six years of formal schooling, and no English. Once in the United States, Dzus stayed with his older sister in Newark, New Jersey, and worked at menial jobs: peeling potatoes, carrying building materials, digging ditches. He quickly set about learning English in night school, then enrolled in a trade school to master lathe operation and mechanical drawing. Once inside the engineer’s world, he never left it, studying automobile mechanics and electricity so successfully that by 1916, according to Bern, “he found himself equipped to think creatively about mechanical problems on a theoretical as well as a practical level.”
As he passed through a series of machinist’s and mechanic’s jobs, Dzus tried to invent his way out of wage slavery. In 1918 he filed for his first patent, on a lathe tool. (The patent was granted four years later to “W. Dross.”) In 1924 he patented an automobile-engine cooling fan. He failed to capitalize on these early inventions, however. By the time of the stock-market crash of 1929, when he was thirty-four, Dzus had opened a garage in Babylon, New York, and seemed to be on his way as a small businessman. But the Depression forced him to close his doors, and he found work in nearby Farmingdale as a toolmaker with the American Airplane and Engine Company, part of the expanding Long Island aircraft industry of the time.
Dzus’s job at this division of the Fairchild Aircraft Company set the stage for the invention that would make him rich. The proximate causes were two changes in aircraft design and manufacturing practice: the transition in airframes from wood to metal and the rapidly spreading use of the “NACA cowl” on the air-cooled radial engines of the day. The National Advisory Committee for Aeronautics (NACA) had shown how a metal covering, suitably sized and shaped, could increase the effectiveness of contemporary radial engines by providing better cooling and minimizing drag. These changes were occurring just as Dzus joined the company, which was struggling to devise fabrication techniques with new aluminum alloys. Dzus’s first triumph came when he eliminated potentially dangerous scratches from the surface of critical airframe components by simply coating them with lacquer before extrusion. After that, says Bern, he “was regularly called in by all of the structural departments as a trouble shooter” and promised twenty-five-dollar cash bonuses for his innovations— which, he claimed, he never received.
EVIDENTLY RECOGNIZING THAT AVIATION MIGHT BE a fertile field for his sort of inventing, Dzus began looking for problems to solve. In 1931 he found one in the NACA cowls on Army fighters that were conducting maneuvers out of his company’s airfields. His curiosity piqued by the rattling of the metal cowls on landing (which, Bern is careful to state, Dzus observed “during lunch and after working hours”), he discovered that they were usually fastened not to the airframe but to the engine itself. The pin-and-post, turnbuckle, and latch-type fasteners that were used to attach the cowls did not counter the effects of the engine’s vibration, which, it was reported, had led to aircraft being grounded or destroyed when the cowls came apart. Dzus concluded that metal fatigue was the chief cause. It developed, he realized, because the fasteners then in use were allowing the cowl’s sections to vibrate at the joints.
The solution Dzus came up with, according to Bern, was “similar in form to a special cranking device which he had designed during his years as an automobile mechanic.” There seems to be no reason to doubt this explanation of the design’s background. Other quarter-turn fasteners, though, such as the Murphy or Common Sense twist-lock types, had been used to secure panels on aircraft since before World War I. These all used a small coil spring underneath the base of the fastener to give retentive force to an upward-protruding “blade,” which snapped into a metal grommet on the upper panel when turned ninety degrees. Dzus’s invention immediately made obsolete this method of securing panels, at least for applications where vibration resistance, close fit, and secure locking were important. It minimized vibration at the joint and also was much more aerodynamic than all previous fasteners, since its spring assembly was inside the lower panel, out of the airflow, with only the slight dome of the Dzus button protruding—and it could be countersunk, if necessary, to provide a flush fit.
Dzus filed his first patent application for his fastener on September 15, 1931, and the patent was granted on April 24, 1934. In the interim he submitted samples to Fairchild. They were approved for use in an experimental aircraft and worked so well that according to his biographer, “without consulting Dzus, the company placed an order with one of its suppliers for a substantial quantity of identical units.” The company and Dzus then engaged in a prolonged wrestling match over ownership of the patent rights. Fairchild claimed rights to anything Dzus invented while he was employed by the company, but Dzus replied that he had devised and built the fastener in his home workshop. The company gave Dzus an ultimatum: Sign over the rights or quit. Dzus quit.
On April 26, 1932, he opened his books as a manufacturer. On May 24 he received his first order, for sixteen fasteners at twenty-five cents apiece, from the Long Island aircraft firm of Amphibions, Inc. Within a few months he was delivering fasteners to Sikorsky and Curtiss-Wright. By the next year Dzus employed eight men. The turning point for this small operation came when the U.S. Army Air Corps made Dzus’s invention a standard fastener for all its aircraft. In 1936 Dzus incorporated his company in West Islip, New York. By the end of the year the Dzus Fastener Company had twenty employees.
World War II vastly expanded Dzus’s operations and fortune. Even an unarmed aircraft like the four-engine Douglas DC-4 needed 827 Dzus fasteners. Despite making as many as fifteen million fasteners a month, the West !slip facility could not meet demand. The War Production Board (WPB) made things worse by misclassifying the factory’s raw-material category in the clothing industry, and it eventually took a congressional hearing to sort things out. After clearing up the misunderstanding with the WPB, Dzus briefly became a minor celebrity, appearing in Time as a “little man with a big idea.” By then he had already arranged for royalty-free production of his fasteners by several large airframe manufacturers.
After the war Dzus’s company continued to expand, and by his death on June 19, 1964, some six thousand variations on his fastener had been developed, including experimental devices designed to aid in orthopedic surgery. His company remained under family ownership until 1988, when it was bought by a British manufacturer that had taken out a license from Dzus fifty years earlier.
DZUS HELD THIRTY-TWO PATENTS, MOST OF THEM related in some way to his fastener. He exemplifies the rare inventor who makes it big on one idea devised at the right place and time—the right place, because central Long Island was a major locus of aviation activity, and the right time, because his invention came at a transition point in the way airplanes were conceived and built. His seemingly simple fastener has yet to be surpassed for a wide variety of applications in complex structures from aircraft to automobiles. Though few who use the Dzus fastener today know the story behind it, they do know what it will do. Consequently, the word Dzus is often used to refer to any quarter-turn-to-lock fastener. There may be a better description of enduring success in the history of invention, but it’s hard to imagine what it might be.