United States Standard thread
Encyclopedia
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
s and washer
s.
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 National Coarse) to describe a fastener that previously would have been designated USS and the Unified Thread Standard uses the term UNF (Unified National Fine) to describe a fastener that would have previously been designated SAE.
where P is the pitch and D is the diameter of the rough stock.
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. 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.
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.
Fastener
A fastener is a hardware device that mechanically joins or affixes two or more objects together.Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container,...
s and washer
Washer
Washer may refer to:People*Mal Washer, an Australian politician*Paul Washer, a Christian preacherOther*Washing machine*Washer *Washer Method, a mathematical formula for finding volume*Washer pitching, an outdoor game...
s.
The USS standard is no longer supported. It, together with the SAE
SAE International
SAE International is an organization for engineering professionals in the aerospace, automotive, and commercial vehicle industries. The Society is a standards development organization for the engineering of powered vehicles of all kinds, including cars, trucks, boats, aircraft, and others.SAE...
fastener standard, was incorporated into the Unified Thread Standard
Unified Thread Standard
The Unified Thread Standard defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada...
. 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 National Coarse) to describe a fastener that previously would have been designated USS and the Unified Thread Standard uses the term UNF (Unified National 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 from. 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 inch screws and larger, the pitch is defined as:where P is the pitch and D is the diameter of the rough stock.
History and use
William SellersWilliam Sellers
William Sellers was a mechanical engineer, manufacturer, businessperson, 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
Franklin Institute
The Franklin Institute is a museum in Philadelphia, Pennsylvania, and one of the oldest centers of science education and development in the United States, dating to 1824. The Institute also houses the Benjamin Franklin National Memorial.-History:On February 5, 1824, Samuel Vaughn Merrick and...
. 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
Association of Licensed Automobile Manufacturers
The Association of Licensed Automobile Manufacturers , originally the Manufacturer's Mutual Association , 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...
developed what would be the SAE 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.
See also
- British Standard WhitworthBritish Standard WhitworthBritish Standard Whitworth is one of a number of imperial unit based screw thread standards which use the same bolt heads and nut hexagonal sizes, the others being British Standard Fine thread and British Standard Cycle...
- "History of standardization" section of the screw thread article
- ISO metric screw threadISO metric screw threadThe ISO metric screw threads are the world-wide most commonly used type of general-purpose screw thread. They were one of the first international standards agreed when the International Organization for Standardization was set up in 1947.-Basic profile:...
- ScrewScrewA screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...
- Screw threadScrew threadA screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...