Screw threads to make landmark history

The second of five anniversary-year landmark ceremonies will take place in Philadelphia during ASME's Summer Annual Meeting next month.

ASME will designate the William Sellers screw-thread standards and the Franklin Institute as an ASME Mechanical Engineering Heritage Site.

The ceremony will take place in the Franklin Institute's Memorial Hall at 5 p.m. on June 12, shortly before the opening reception of SAM at the recently renovated institute in Philadelphia. ASME's heritage is entwined with Benjamin Franklin's early development of standards and leadership in the mechanical arts, which will be celebrated.

The landmark honors William Sellers' (1824-1905) screw threads presentation at the Franklin Institute in 1864. During the 45-minute ceremony, ASME President Harry Armen will present a plaque to Dennis Wint, president of the Franklin Institute.

Following the ceremony, attendees will be invited to ASME's opening reception, which will be held in the adjacent rotunda.

The plaque will read: "Historic Mechanical Engineering Landmark United States Standard Screw Threads, 1864.

"In 1864, an American maker of machine tools, William Sellers, developed a comprehensive system for the design of screw threads for machine bolts and hex nuts. Within the year, Sellers's system had been endorsed by Philadelphia's Franklin Institute, then America's leading research and development organization in mechanical engineering.

"Over subsequent decades, the Sellers or Franklin Institute threads became a national standard. This rationally elegant yet simple system of fasteners boosted productivity, simplified machinery repairs, and united diverse machine makers and users from coast to coast. Known today as the United States Standard screw threads, William Sellers's legacy is still widely used."

The landmark designations this year are part of the events commemorating ASME's 125th anniversary. For more about the anniversary celebrations, visit www.asme.org/anniversary.

Prior to Sellers's development, America was operating in an era of machinery infatuation. Sophisticated technologies at that time included the development of textile machines, metal planers, steam engines, locomotives and rotary printing presses, among others.

That infatuation, however, quickly turned to frustration when those machines broke down. The country lacked any national or industry standards for the most basic mechanical elements: the nuts and bolts that created a functional machine from disparate parts. So when a bolt broke or a nut was lost, the user had to make a new one to fit its mate or send for a replacement from the builder.

No one could deny the value of a national standard for these essential fasteners. Indeed, by that time, the world's industrial leader, Great Britain, was adopting a comprehensive system of screw threads promulgated in 1841 by that nation's leading maker of machine tools, Joseph Whitworth.

His American counterpart, tool builder William Sellers of Philadelphia, understood the value of Whitworth's standard, a clear improvement over the various "mongrel" threads that U.S. machinery makers had adopted. But Sellers decided to improve upon Whitworth's approach, creating a system of threads adapted to American needs.

In April1864, Sellers laid out his proposed system of screw threads in a paper delivered at Philadelphia's Franklin Institute. Sellers simplified Whitworth's design by adopting a thread profile of 60 degrees, versus 55 degrees, which was easier for ordinary mechanics and machinists to cut. In addition to this profile, Sellers offered systematic approaches to thread pitch — the number of threads per inch — form and depth, as well as rules to proportion hex nuts for each fractional size from 1/4-inch to 6-inch-diameter bolts.

In this era, before the founding of ASME, the Franklin Institute was America's leading forum for developing the art and science of mechanical engineering. William Sellers was its president.

On Dec. 15, 1864, a special committee of the Institute endorsed the Sellers or Franklin Institute threads. To aid their adoption throughout the United States, the Institute lobbied the U.S. Army, Navy (whose Bureau of Steam Engineering was a leading mechanical innovator) and the master mechanics of America's largest railroads.

The new thread standards did not sweep the nation overnight. The inertia of old approaches was difficult to surmount, while thorough adoption required newly precise taps and dies as well as reliably dimensioned steel bar stock. But by the 1880s, the system had triumphed, as machines with interchangeable parts from typewriters to locomotives flooded the national economy.

Known originally as the Sellers or Franklin Institute threads, they became the United States Standard threads. Other systems of screw threads have since come into widespread use. But down to the present day, William Sellers's innovation remains a ubiquitous standard.

Take a quarter-inch nut from a Portland, Maine, hardware store and it will reliably fit a quarter-inch bolt in Portland, Ore. The economy and simplicity of this elegantly rational system represents William Sellers's legacy and the enduring quality of fine mechanical engineering.

 

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