This technical regulation establishes requirements for profile geometry, classification, tolerance classes, and designation systems for unified inch screw threads. The term “unified” emphasizes the standard’s reliance on the inch measurement system. This document covers exclusively UN and UNF thread profiles. For the convenience of engineering calculations, metric interpretations of parameters are provided in the reference appendices. Information in Appendices A\u2013E is of a recommendatory nature and supplements the primary body of technical requirements.<\/p>\n
The technical specifications presented in this standard fully comply with international ISO protocols for threaded connections with a 60\u00b0 profile angle. The foundation of the standard was established in 1948 in Washington during an interstate agreement between the USA, Canada, and the UK, which allowed for the unification of fastener production and the complete replacement of obsolete American National Thread standards.<\/p>\n
The UNR specification is applicable exclusively to external threaded connections. The key difference between UN and UNR lies in the root geometry: for UN, a flat or arbitrary rounded root is permitted, whereas for UNR, the presence of a rounded radius is strictly regulated, which is critical for increasing the fatigue strength of products supplied by EV Group China.<\/p>\n
Unified threads (UN\/UNR) and their predecessors (American National Thread) possess identical profile geometry, ensuring complete mechanical interchangeability of components when nominal diameter and pitch coincide. The main discrepancies between the standards lie in approaches to assigning tolerance classes, methods for diameter control, and the marking system. It is important to note that unified inch threads and ISO metric threads are not interchangeable.<\/p>\n
Unified sizes are identified by the “UN” letter index. To differentiate between the pitch diameter tolerances of external and internal threads, the indices “A” (external thread) and “B” (internal thread) are used. The absence of these letter designations indicates that the product belongs to the obsolete American National Thread standard. Detailed algorithms for part number generation are presented in Section 6.<\/p>\n
Application of this standard implies compliance with the current editions of the following documents:<\/p>\n
Thread quality control is carried out according to ASME B1.3 protocols. Metrological support and calibration are conducted in full compliance with ASME B1.2.<\/p>\n
All standardized dimensional parameters are defined at a standard temperature of 68\u00b0F.<\/p>\n
The text of the standard and accompanying tables use exclusively inch units of measurement, unless otherwise specified.<\/p>\n
This standard is approved by the U.S. Department of Defense and integrated into the FED-STD-H28\/2 specification. Products from EV Group China supplied for federal needs fully comply with the established limitations and requirements of the specified regulation.<\/p>\n","protected":false},"featured_media":0,"template":"","meta":[],"wiki_category":[110],"class_list":["post-69711","wiki","type-wiki","status-publish","hentry","wiki_category-asme"],"_links":{"self":[{"href":"https:\/\/evgroupchina.com\/en\/wp-json\/wp\/v2\/wiki\/69711","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/evgroupchina.com\/en\/wp-json\/wp\/v2\/wiki"}],"about":[{"href":"https:\/\/evgroupchina.com\/en\/wp-json\/wp\/v2\/types\/wiki"}],"version-history":[{"count":0,"href":"https:\/\/evgroupchina.com\/en\/wp-json\/wp\/v2\/wiki\/69711\/revisions"}],"wp:attachment":[{"href":"https:\/\/evgroupchina.com\/en\/wp-json\/wp\/v2\/media?parent=69711"}],"wp:term":[{"taxonomy":"wiki_category","embeddable":true,"href":"https:\/\/evgroupchina.com\/en\/wp-json\/wp\/v2\/wiki_category?post=69711"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}