The thread of the 8-UN thread table belongs to the Unified National Fixed Pitch Series (UN), which in turn is part of the Unified National Thread Series (UTS). This is a series of American thread standards that are defined and monitored by the American National Standards Institute (ANSI). The values in the 8-UN thread table are based on the ANSI B1.1 standard. As you can see from the 8-UN thread table, the special feature of the UN series is the unchanging number of threads per inch. This means that all thread sizes have the same number of threads, in the case of the 8-UN threads in the table this is 8 threads. The UN series also includes threads with 4, 6, 12, 16, 20, 28 and 32 threads per inch.
The 8-UN thread is an imperial thread with a 60° flank angle. As with all UN threads, the 8-UN thread table only covers those combinations of outside diameter and pitch per inch that are not already available in other thread standards such as UNC, UNF or UNEF. The 8-UN thread table therefore only contains special pitches for special applications. It is also noticeable that there are significantly fewer thread sizes in the 8-UN thread table than in the standards for other UTS threads. Due to the fixed number of threads per inch, not every combination of pitch and outside diameter makes sense. Only those variants that prove to be practical in use have been included in the 8-UN thread table.
The table for the 8-UN thread only contains thread sizes from an outside diameter of 1 1/16". The thread designation is made up of the outside diameter and the abbreviation 8-UN. Unlike other UTS threads, the number of threads per inch no longer needs to be added to the thread designation in the 8-UN thread table, as this is always 8. In our 8-UN thread table, we have listed the outer diameter in mm in addition to the information in inches if you want to work with metric data. In the 8-UN thread table you will also find the conversion of the number of threads per inch into mm, which in this case corresponds to 3.175 mm.