UNF Thread (USA)

The UNF thread is the American fine thread of the Unified Thread Standards (UTS). Similar to the metric system, there is a distinction between coarse and fine threads in American thread standards. The acronym UNF stands for Unified National Fine. However, besides the UNEF thread, the UNF thread is just one of two fine thread variants often used for fastening screws and nuts. In addition to the USA and Canada, the UNF thread is also widespread in many other countries around the world, including Australia, India, Japan, and Pakistan.

All UTS thread standards are designed by the American Society of Mechanical Engineers (ASME) and overseen by the American National Standards Institute (ANSI). The UNF thread is found under the standard ANSI/ASME B1.1.

The UNF thread is an inch-based thread. Accordingly, all measurements are given in inches, and the pitch is specified in threads per inch. However, this specification can be easily converted into a pitch in mm. The flank angle is 60°, which not only corresponds to other UTS threads but also to many other standard fastening thread norms such as the metric ISO thread.

The thread designation for the UNF thread consists of the external diameter, the number of threads per inch, and the acronym UNF. All UTS threads have a different designation for all thread sizes with an external diameter below 1/4". In these cases, the specification of the external diameter is replaced by a fixed numerical value. For the UNF thread, this applies to ten thread sizes, which are numbered from 0 to 12. The correct designation would then be, for example, #1 – 72 UNF. For sizes above the threshold, the designation for a UNF thread would be, for example, 7/8" – 14 UNF.

In the thread table for the UNF thread, the external diameter in inches and the number of threads per inch are listed. In the table below, we have additionally translated both values into a metric measurement. Furthermore, we have added the core hole diameter to the table, which you should definitely consider when cutting a UNF thread. To get to the suitable taps and dies for all sizes of the UNF thread, click on the corresponding link in the table.