It is very common to find the use of the unified national system for thread in the United States and in Canada u like most other countries that make use of the metric thread system. Research and studies have shown that about 60% of the screw threads used in the US are still inches based. We can define thread system as a set of various thread designations which represent different thread sizes that helps define the thread geometry. The UNEF thread gauges which in its full meaning denotes the unified extra fine thread is a unified form thread designation on its own.
There is a fixed number if TPI for a special diameter for threads in the UNEF thread gauge. One vital feature this thread possess is that it has a slightly higher breaking load capacity than he UNC thread gauge. This is as a result of the larger tensile stress area and lesser thread depths. Where needed, the smaller leads gives room for fine adjustment. Even the allowances/tolerance class for the UNEF Thread gauge are designated by the letter ‘A’ preceded by a number for example, class 1A, 2A, or 3A. The internal Unified national extra fine threads are designated by the letter ‘B’ preceded by a number for example, 1B, 2B, or 3B. Therefore in this thread system, a 1A thread ring gage fits a 1A thread set plug.
On the other hand, the unified national fine thread known as the UNF thread gauge also has a fixed number of threads per inch on a special diameter. Almost having the same characteristics of the UNEF Thread gauge, the UNF thread gauges slightly differs from the unified national extra fine thread gauge by… However, both threads share some other similar features. Such features common to them are given below:
- They both allow more precise adjustment because of smaller helix angle.
- They equally have higher strengths in tension because of their larger tensile stress area.
- In terms of cutting, the UNEF Thread gauge and the UNF thread guage are easier to tap in harder materials. Even where their length of engagement is limited, fine threads provide greater strength. While the shorter thread depth of the two threads allows threading in thin wall applications.
The Unified Extra Fine Thread, which is used for special purposes has a flank angle of 60°. If the fine thread is longer than the engagement length, the unified extra fine thread is useful. It can also be used in applications where one can use fine thread. While on the other hand, the UNF thread gauge is used for applications that needs higher tensile strength over the corse thread series and where thin wall are needed. The basic profile of all unified thread system including the UNC, the UNF, and the UNEF is the same as that of ISO metric screw threads.