United States Standard thread (USS thread), also known as Sellers Standard thread, Franklin Institute thread and American Standard thread, is a standard for inch based threaded

fastener A fastener (US English) or fastening (UK English) is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or disman ...

s and

washer Washer most commonly refers to: *Washer (hardware), a thin usually disc-shaped plate with a hole in the middle typically used with a bolt or nut *Washing machine, for cleaning clothes Washer may also refer to: *Dishwasher, a machine for cleani ...

s. The USS standard is no longer supported. It, together with the

SAE SAE or Sae may refer to: Science and technology : * Selective area epitaxy, local growth of epitaxial layer through a patterned dielectric mask deposited on a semiconductor substrate * Serious adverse event, in a clinical trial * Simultaneous Aut ...

fastener standard, was incorporated into the

Unified Thread Standard The Unified Thread Standard (UTS) defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada. It is the main standard for bolts, nuts, and a w ...

. However, the term, ''USS'', continues to be used occasionally today to describe inch based threaded fasteners with a coarse thread pitch and inch based washers that are a little bit larger than the corresponding SAE washer. The Unified Thread Standard uses the term UNC (Unified Coarse) to describe a fastener that previously would have been designated USS and the Unified Thread Standard uses the term UNF (Unified Fine) to describe a fastener that would have previously been designated SAE.

Thread form

The thread form is defined by flats at the tip and root of the thread form. This flat length is defined as the pitch divided by eight. The thread depth, which is from flat to flat is 0.6495 times the pitch. For screws and larger, the pitch is defined as: :

P = 0.24 \sqrt  - 0.175

where ''P'' is the pitch and ''D'' is the diameter of the rough stock.

History and use

William Sellers William Sellers (September 19, 1824 – January 24, 1905) was a mechanical engineer, manufacturer, businessman, noted abolitionist, and inventor who filed more than 90 patents, most notably the design for the United States standard screw thread ...

originally developed the USS thread, and set forth many of its details in his paper, "A System of Screw Threads and Nuts", presented in April 1864 to the

Franklin Institute The Franklin Institute is a science museum and the center of science education and research in Philadelphia, Pennsylvania. It is named after the American scientist and statesman Benjamin Franklin. It houses the Benjamin Franklin National Memori ...

. In 1898, the standard for metric threaded fasteners was established. The metric standard used the same thread geometry as the USS standard but differed in that the dimensions and pitch were based on metric units. In 1906, the A.L.A.M developed what would be the

thread standard for threaded fasteners based on the USS standard but with a finer thread pitch. A Unified Thread Standard UNC thread is mechanically interchangeable with a USS thread of the same diameter. However, there are tolerance and other differences between a thread compliant with the USS thread and a Unified Thread Standard UNC thread. The Unified Thread Standard for quarter inch and larger threaded fasteners was adopted on November 18, 1948, and was subsequently adopted for smaller thread series.

References

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External links

The United States Standard Screw Threads (1864)Text of Seller's presentation to the Franklin Institute, April 21, 1864
Screws Thread standards Standards of the United States

Thread form

History and use

See also

References

External links