8-UN Thread (USA)
The 8-UN thread is an American thread standard with a constant pitch. It is just one of a set of such thread standards with a fixed number of threads per inch. In the case of the 8-UN thread, this value is 8, but the series of UN threads also includes threads with 4, 6, 12, 16, 20, 28, and 32 threads per inch. The abbreviation UN stands for Unified National. Like most common American thread standards, it was defined by the American Society of Mechanical Engineers (ASME) and is monitored by the American National Standards Institute (ANSI). The corresponding standard is ANSI/ASME B1.1.
The 8-UN thread is an imperial thread. The flank angle is 60°. The thread designation is composed of the outer diameter in inches and the abbreviation 8-UN. Unlike other thread standards in the Unified Thread Standard (UTS) series, the pitch is part of the thread identification and thus does not need to be stated again.
In the thread table for 8-UN threads, only combinations of outer diameter and number of threads that are not already covered by the UNC, UNF, or UNEF thread standards are included. So, if you do not find the required outer diameter in the 8-UN thread table, you should look at the other UTS threads. It is very likely that the desired thread will be in one of these tables.
The table for the 8-UN thread includes sizes from 1 1/16″ to 4″ outer diameter. As with all UN series threads with constant pitch, the range is limited by this fixed pitch, as not every combination is practical. Below is a table with the dimensions for the 8-UN thread in inches and converted to mm. Also listed is the core hole diameter you need for the pilot hole. Click on the corresponding link to get to the appropriate die or tap for the desired 8-UN thread.