Brief introduction of American thread
American thread is also called unified thread. 1864, American Willie Cetus (Willian? Sellers) formulated American national thread (N) with reference to British Wyeth thread standard system. These two kinds of threads are very similar in diameter and pitch series and tolerances.
Second, the origin of American thread
The tooth profile of American national thread (tooth profile angle 60, flattening height H/8) is different from that of Wyeth thread (tooth profile angle 55, flattening height H/6). American national thread is widely used in areas and industries influenced by American industry. In World War II, due to the inconsistent thread standards used by the Allies, logistics supply was difficult, which caused serious economic losses and casualties to the Allies. After World War II, the United States, Britain, Canada and other allies immediately set out to formulate a unified thread standard among allies, and promulgated the unified thread standard in 1948.
At that time, the economic strength and military strength of the United States dominated the allied forces, so the unified thread was mainly formulated according to the national thread standard of the United States, and the first letter "U" of the unified thread code "UN" came from the "unification" among the allies; The last letter "n" comes from the code name "n" of American national thread. Since then, unified thread has occupied the original use market of Wyeth thread in Britain.
Third, the thread code of American thread
Coarse tooth series UNC,
Fine tooth series UNF,
Ultra-fine tooth series UNEF,
Fixed pitch series UN
Four, the United States thread representation methods and standards
Marking method: thread diameter-number of teeth per inch series code-accuracy grade example: coarse tooth series? 3/8— 16? 2A United Nations Headquarters
Fine tooth series? 3/8—24? United Nations Foundation-2A
Extra fine tooth series? 3/8—32? UNEF—2A
Fixed distance series? 3/8—20? United Nations -2A
The first digit, 3/8, indicates the thread outer diameter in inches, which is converted into metric unit mm multiplied by 25.4, that is, 3/8× 25.4 = 9.525mm; The second and third digits 16, 24, 32 and 20 are the number of teeth per inch (the number of teeth on a length of 25.4mm); The text codes UNC, UNF, UNEF and UN after the third digit are series codes, and the last two digits 2A are precision grades. UNC: uniform coarse thread
The Unified Thread Standard (UTS) provides a standard thread form and a series of other data, including tolerances, tolerances and names, which are commonly used in the United States and Canada. Like ISO metric thread commonly used in other parts of the world, the tooth profile angle is 60, except that the main dimensions (outer diameter and pitch) of UTS thread are expressed in inches and in fractions, not in millimeters. UTS is currently managed and controlled by american society of mechanical engineers/American National Organization for Standardization (ASME/ANSI). ?
Above, we introduced four aspects of information about American thread, namely, the introduction of American thread, the origin of American thread, the expression method of American thread and the thread code of American thread. Through the study of the above knowledge, we know that American thread is a kind of thread, also called unified thread. According to different application scenarios and shape parameters, the expression and code are also different. American thread is one of the American standard threads, so it is widely used in many places in the production and life fields of the United States and other countries.