Sellers thread
The Sellers thread is a historical threading system from the USA. Its inventor, engineer, and entrepreneur William Sellers (1824-1905), is considered the American counterpart to Joseph Whitworth, the father of the British thread standards still named after him today. Sellers presented his design in 1864 to the Franklin Institute in Philadelphia, where he served as president. At that time, the Franklin Institute was the most important research institute in the field of mechanical engineering in the USA. Despite this impressive backing, it took until the 1880s for the Sellers thread to become widely adopted nationwide. The threading system is also known under the designations United States System and Franklin Institute System. It is also the precursor to today's UN thread.
The Sellers thread is an inch-based thread. Accordingly, all measurements are given in inches, and the pitch is specified in threads per inch. It has a flank angle of 60°, which distinguished the Sellers thread from its main competitor at the time, the Whitworth thread. Also unique to the Sellers thread was the profile with flattened peaks and valleys, which made it easier for inexperienced mechanics to cut the thread.
The thread designation for the Sellers thread is composed of the external diameter in inches and the pitch in threads per inch. A typical designation for a Sellers thread size would thus be 3/8" - 16.
The thread table for the Sellers thread covers sizes from 1/4" up to 6". In the table, in addition to the thread designation, the external diameter and number of threads per inch are listed separately. In the thread table for the Sellers thread below, we have supplemented both of these figures with their metric equivalents. Also listed is the core hole diameter in mm. If you need dies or taps for the Sellers thread, please contact our customer service.