The thread in the UN thread table is an American thread type with a special pitch. The UN thread belongs to the Unified National Thread Series (UTS), which is defined and monitored by the American National Standards Institute (ANSI). The dimensions presented in the "UN thread" table correspond to the ANSI B1.1 standard. The UN thread describes a series of thread types with a fixed pitch. This means that the number of threads per inch remains constant even as the thread size increases. As a result, the UN thread from the table achieves combinations of outside diameter and number of threads per inch that are not covered by other UTS thread types such as the UNC, UNF or UNEF thread.
UN threads are available with 4, 6, 8, 12, 16, 20, 28 and 32 threads per inch. We have presented some of the most common combinations in our UN thread table. The most common variants 8-UN, 12-UN and 16-UN are described in more detail in separate UN thread tables. Due to the unchangeable pitch, the UN thread table covers fewer thread sizes than other UTS thread types. With very few threads per inch, the thread would otherwise be too coarse and would not prove practical in use.
Also missing from the UN thread table are those combinations of outside diameter and number of threads per inch that are already covered by other UTS thread tables. For example, a thread with 3/4" outside diameter and 20 threads per inch is already part of the UNEF standard and therefore no longer appears in the UN thread table. As a general rule, pitch/outer diameter combinations of thread types UNC, UNF and UNEF always have priority. Only those variants that are not defined elsewhere are listed in the UN thread table.
The UN thread is an imperial thread with a 60° flank angle. The thread designation is made up of the abbreviation UN, the outside diameter in inches and the number of threads per pitch. You can find all these details in our UN thread table. You will also find the transfer of the data for the outside diameter in mm as well as the conversion of the number of threads per inch into the pitch in mm.