Imagine it is the 40’s in America. Industry is booming and globalization is making the world evermore connected. Global standards are beginning to be established for manufacturing industries, and the “American Standard” is set – quite literally. In November 1948 the Unified thread was agreed upon by the United Kingdom, the United States and Canada to be used as the single standard for all countries using inch units. Out with the old, and in with the new standard!
Step Aside, American National System
The American Standard B1.1-1949 was the first American standard to cover the specifications of the Unified Thread Series established by the United Kingdom, Canada, and the United States. These “unified” standards were established to create more interchangeability between these three industrial power houses. As transportation and trade between these nations became more fluid, so did transfer of machinery, knowledge, and best practices. Manufacturing took a global stage, and so did manufacturing standards.
Unified and Interoperable
The greatest advantage of these new standards was that, largely speaking, the unified threads agreed upon by the three nations were not dramatically different from the previous, uniquely American specifications. The unified threads have substantially the same thread form and are mechanically interchangeable with the former American National threads of the same diameter and pitch.
There were some key differences between the two, namely the application of allowances, the variation of tolerances with size, the difference in amount of pitch diameter tolerance on external and internal threads, and differences in thread designation. But change isn’t all bad! In fact, in the unified system, the allowance is provided on both the Classes 1A and 2A external threads whereas in the previous system only the Class 1 external thread has an allowance. Moreover, in the unified system, the pitch diameter tolerance of an internal thread is 30% greater than that of the external thread, whereas they are equal in the American National System.
Designing a New Standard
The new, unified standard was designed to correct several challenges of the American National System. For example, the former standard had a few production difficulties: the tolerances of the product were practically absorbed by the combined tool and gage tolerances, leaving little for a working tolerance in manufacture. Furthermore, pitch diameter tolerances on the external and internal threads were equal, which also presented challenges. The new unified standard offered a 30% larger pitch diameter tolerance than the 1A, 2A, and 3A external threads.
Modern Era
Of course, technology has improved greatly since the late 40’s. While thread design and manufacturing has become more precise, these standards and best practices remain. Navigating these complexities is nonetheless a challenge, and that is where a trusted authority like Thread Check Inc. can expedite your workflows! Do you have a question about your design needs or best practices? Give us a call at 1-800-767-7633 or email us at [email protected] to get started today.