The Self-Taught Machinist Who Decided How Every American Screw Would Turn

William Sellers was a self-taught Philadelphia machinist who, in 1864, proposed a new American screw thread standard: a 60-degree angle with flat crests and roots, chosen specifically because it was easier for an ordinary machinist to cut than the rounded British Whitworth thread already in wide use. The Franklin Institute endorsed it within months, but it was the Pennsylvania Railroad's 1869 decision to make it mandatory for every bolt it bought that forced the rest of American industry to follow. That standard became the American Standard Thread in 1924 and formed the basis of the 1948 Unified Thread Standard still used today. Sellers also built the Edge Moor Iron Company (which supplied the Brooklyn Bridge's structural steel) and reorganized Midvale Steel, the plant where a young machinist named Frederick Winslow Taylor invented scientific management. Yet the company itself passed through six different owners across the 20th century, finally surviving today only as a small employee-owned repair shop in Rochester, New York. This is Precision Valley — if you want more stories like this, subscribe.