In 1841, Joseph Whitworth, an Englishman, proposed the world's first national thread standard (BS84, Wyeth thread B.S.W. and B.S.F.), thus establishing the technical system of thread standards. The National Thread (N) standard in the United States was developed based on the British Wyeth thread. After World War II, it was transformed into the Unified Thread (UN) commonly used by the Allied Powers during World War II. This is the world's first international standard recognized by an international organization. What is the pipe thread standard in the United States. The metric ordinary thread (M) is derived from the American national thread (N) and has been widely used on the European continent, and has been included in the ISO standard. When the metric system of units is established as the international legal measurement system.
Metric threads refer to threads measured in metric units and invented by European metric countries, with their length dimensions measured in metric units. So also known as "metric thread", American and British threads refer to threads invented by the United States and the United Kingdom respectively, and their pitch is generally given in the form of the number of threads per inch.Also known as metric thread, the pitch is measured in millimeters. Common types include regular threads (with a tooth angle of 60 °), trapezoidal threads (with a tooth angle of 30 °), serrated threads (with a tooth angle of 33 °), and square threads. The types of tolerance zones for metric ordinary threads are much more than those for American standard threads.
