Internal or external symbol (A is for external threads, B is for internal threads), followed by a space.Number of threads per inch, followed by a space.Major diameter in fraction or three place decimal form.Internal thread notes are given on the end view, with a pointer to the solid circle.Ī thread note should contain the following information: A thread note must be included on all threaded parts, with a leader line to the external thread or to an internal thread in the circular view.Įxternal thread notes are given in the longtitudinal view. Threads are only symbolically represented on drawings therefore, thread notes are needed to provide the required information. Class 3 - a very high-quality threaded fastener with a close fit, used for precision tools and for high stress and vibration applications.Class 2 - a high-quality, general purpose, commercial class of fit for bolts, nuts, and screws widely used in mass production.Class 1 - a loose fit where quick assembly is required and looseness or play between parts is acceptable. There are three classes of fit established by ANSI for general use. It is used when the Coarse, Fine, Extra-Fine Series do not meet the design requirements, and within these series, preference should be given to the 8, 12, and 16 thread series. C onstant pitch series threads are for special purposes, such as large-diameter or high-pressure environments.Extra fine series fasteners are used when the length of engagement is short and the application calls for high degrees of stress.These fasteners are used extensively in the aerospace and automotive industries. Fine series fasteners are used when a great deal of force is necessary for assembly, and are designated NF or UNF.Coarse series fasteners are used for quick assembly or disassembly of cast iron, soft metals, and plastic, and are designated NC or UNC.The constant pitch series is specified by writing the number before the form designation (4, 6, 8, 12, 16, 20, 28, 32). When used with the Unified thread, they are abbreviated UNC, UNF, and UNEF. The thread series refers to the standard number of threads per inch, and there are four classes: coarse (C), fine (F), extra fine (EF), and constant pitch. The knuckle thread is usually rolled from sheet metal or cast, and it is used for lightbulb bases, bottle caps, and glass jars.The square, Acme, and buttress threads are used to transmit power in gearing and other types of machines. The metric thread is the international standard thread, similar in shape to the American National thread.A variation on the Unified thread is the Unified National Round thread, abbreviated UNR.The Unified thread is the current standard used in the United States, Canada, and England.The American National thread replaced the sharp-V thread and is stronger than the sharp-V thread.The sharp-V thread was originally developed by William Sellers (Septem– January 24, 1905), a mechanical engineer, manufacturer, businessman, and inventor who filed more than 90 patents.Many types of thread forms have been developed. Thread form is the shape or profile of a screw thread. To specify a thread using the English system, you must provide a minimum of five pieces of information: A threaded fastener is a mechanical fastener used to join two or more parts. One of the most common methods used for fastening is mechanical fastening, a process that uses manufactured devices such as screws, pins, or rivets to hold parts of an assembly together. Fastening is a method of connecting or joining two or more parts together, using processes or devices.
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