#234 The United States Standard Screw Threads


First US system of standardized screw threads

Photo of William Sellers

William Sellers (1824-1905) of Philadelphia was inspired by Great Britain's adoption of a comprehensive system of screw threads promulgated in 1841 by that nation's leading maker of machine tools, Joseph Whitworth (1803-1887). He understood the value of Whitworth's standard, a clear improvement over the various "mongrel" threads that U.S. machinery makers used, but Sellers decided to improve upon Whitworth's approach, creating a system of threads adapted to U.S. needs.

In April 1864 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.

Sellers was president of The Franklin Institute, America's leading forum for developing the art and science of mechanical engineering. On December 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.

By the 1880s, the new system of standard screw threads became widespread as machines with interchangeable parts, from typewriters to locomotives, flooded the national economy. This rationally elegant yet simple system of fasteners boosted productivity, simplified machinery repairs, and united diverse machine makers and users from coast to coast. They are still widely used, known as the United States Standard Screw Threads.


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Landmark Location

William Sellers Screw Thread Standard at the Franklin Institute Philadelphia, PA

Visiting Info

Regular hours.

Related Links

The Franklin Institute

Ceremony Notes

June 12, 2005. ASME President Harry Armen presented the bronze plaque to the Franklin Institute.

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