Evolution of Thread Standards: From Whitworth to Unified to ISO — and Why It Still Causes Problems
Introduction Threaded fasteners are the backbone of mechanical assembly, yet the standards governing their design have evolved through a complex history. From the earliest British Whitworth threads to the Unified Thread Standard (UTS) and today’s ISO metric threads, each standard was born from industrial necessity and geopolitical forces. This whitepaper traces the development of these major thread standards and examines why, despite decades of standardization, thread incompatibilities continue to plague global operations. Technical comparisons of thread geometry and fit are presented, and real-world examples illustrate how mixing standards leads to [...]