United States Standard thread

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United States Standard thread (USS thread), also known as Sellers Standard thread, [1] Franklin Institute thread [1] and American Standard thread, [2] is a standard for inch based threaded fasteners and washers.

Fastener hardware device that mechanically joins or affixes two or more objects together and used to create non-permanent joints

A fastener or fastening 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 dismantled without damaging the joining components. Welding is an example of creating permanent joints. Steel fasteners are usually made of stainless steel, carbon steel, or alloy steel.

Washer (hardware) thin plate with a hole, normally used to distribute the load of a threaded fastener

A washer is a thin plate with a hole that is normally used to distribute the load of a threaded fastener, such as a bolt or nut. Other uses are as a spacer, spring, wear pad, preload indicating device, locking device, and to reduce vibration. Washers often have an outer diameter (OD) about twice their inner diameter (ID), but this can vary quite widely.


The USS standard is no longer supported. It, together with the SAE fastener standard, was incorporated into the Unified Thread Standard. 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.

SAE International Standards Body

SAE International, initially established as the Society of Automotive Engineers, is a U.S.-based, globally active professional association and standards developing organization for engineering professionals in various industries. Principal emphasis is placed on transport industries such as automotive, aerospace, and commercial vehicles.

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 wide variety of other threaded fasteners used in these countries. It has the same 60° profile as the ISO metric screw thread, but the characteristic dimensions of each UTS thread were chosen as an inch fraction rather than a millimeter value. The UTS is currently controlled by ASME/ANSI in the United States.

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. [3] For 14-inch (6.4 mm) screws and larger, the pitch is defined as:

where P is the pitch and D is the diameter of the rough stock. [1]

History and use

William Sellers 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. In 1898, the standard for metric threaded fasteners was established. [4] 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 SAE thread standard for threaded fasteners based on the USS standard but with a finer thread pitch. [5] [6]

William Sellers American businessman

William Sellers was a mechanical engineer, manufacturer, businessman, and inventor who filed more than 90 patents, most notably the design for the United States standard screw thread. As president of the Franklin Institute in Philadelphia, Pennsylvania, Sellers proposed the adoption of a system of screw threads which was easier for ordinary mechanics and machinists to cut than a similar design by Joseph Whitworth. For many years, he led the machine tool firm of William Sellers & Co., which was a very influential machine tool builder during the latter half of the 19th century.

Franklin Institute Science museum in Philadelphia, Pennsylvania

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, and houses the Benjamin Franklin National Memorial. Founded in 1824, the Franklin Institute is one of the oldest centers of science education and development in the United States.

Association of Licensed Automobile Manufacturers

The Association of Licensed Automobile Manufacturers (ALAM), originally the Manufacturer's Mutual Association (MMA), was an organization originally formed to challenge the litigation of the fledgling automobile industry by George B. Selden and the Electric Vehicle Company. Ultimately, the organization took advantage of its power and became Selden's greatest ally. In exchange for favorable royalty rates, the group gained the power to litigate and exclude other manufacturers from licensing, making them the most powerful group in the early automotive industry.

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. [7] The Unified Thread Standard for quarter inch and larger threaded fasteners was adopted on November 18, 1948, [8] and was subsequently adopted for smaller thread series.

See also

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  1. 1 2 3 Adt, Howard. Screw Thread Production to Close Limits. p. 7. Retrieved 2009-01-16.
  2. "History of screw threads" . Retrieved 2011-04-24.
  3. American Railway Master Mechanics' Association (1916). Report of proceedings of the annual convention of the American Railway Master Mechanics' Association. 49. American Railway Master Mechanics' Association. p. 71.
  4. Oberg, Erik; Jones, Franklin D.; McCauley, Christopher J.; Heald, Ricardo M. (2004), Machinery's Handbook (27th ed.), Industrial Press, p. 1726, ISBN   978-0-8311-2700-8.
  5. The Society of Automobile Engineers 1912 Transactions Part II, pages 43-44 . Retrieved 2009-01-17.
  6. Browning's Industrial Magazine, page 590. The Browning Press. Retrieved 2009-01-27.
  7. Oberg (1988). Machinery's Handbook 23rd edition. p. 1479.
  8. National Bureau of Standards. "Screw-Thread Standards for Federal Services, pages 10-12" (PDF). Retrieved 2009-01-16.