William Sellers & Co. was an iron works that manufactured machine tools used for turning, planing, shaping, drilling, boring, or cutting metal or wood. The company was founded in 1848 as Bancroft & Sellers by Edward Bancroft (1811-1855) and William Sellers (1824-1905).

William Sellers, a member of the illustrious Sellers family of inventors and mechanicians and one of America's leading mechanical engineers, was born in Upper Darby, Pennsylvania, on September 19, 1824. Sellers attended a private school run by his family, and between the ages of 14 and 21 served his apprenticeship in the Wilmington, Delaware, machine shop of his uncle, J. Morton Poole (1812-1879). In 1845, he took charge of the shop of Bancroft, Nightingale & Co. in Providence, Rhode Island. Sellers returned to Philadelphia and set up his own machine shop in 1847. A year later, he was joined by Edward Bancroft as Bancroft & Sellers.

Upon Bancroft's death in 1855, the firm was reorganized as William Sellers & Co., including his brother, John Sellers Jr. (1826-1906), and his cousin, Coleman Sellers (1827-1887). The Sellers firm was one of the foremost American machine shops. Sellers himself obtained over ninty patents covering machine tools, including the spiral-geared planer, rifling machines, and injectors for steam locomotives and boilers.

Sellers served as president of the Franklin Institute from 1864 to 1867. It was here that he delivered his influential paper urging the adoption of a standard system of screw threads, an essential ingredient of interchangeable parts. His proposed system was adopted by the U.S. Government in 1868 and the Pennsylvania Railroad in 1869, leading to its quick, universal acceptance.

Besides his machine shop, Sellers organized the Edge Moor Iron Company in 1868. It became a major producer of structural steel and ironwork, providing materials for the Centennial Exposition and the Brooklyn Bridge. In 1873, he reorganized the William Butcher Steel Works in Nicetown into the Midvale Steel Company, turning it into one of the leading producers of heavy steel forgings, ordnance, and armor plate.

Sellers was also a trustee of the University of Pennsylvania from 1868 until his death and was a member of the National Academy of Sciences, the American Philosophical Society, and other professional societies.

The Sellers firm was incorporated in 1886. It continued to function until April 9, 1947, when the machine tool division was sold to the Consolidated Machine Tool Corporation and relocated to Rochester, New York.