This section provides an overview for unified thread standards as well as their applications and principles. Also, please take a look at the list of 10 unified thread standard manufacturers and their company rankings.
Table of Contents
A unified thread standard is one of the inch threads whose basic dimensions are standardized in inches and whose thread angle is 60°.
Metric screws are standardized in metric units. In addition to the unified thread standard, there is the Witt screw, which is an inch screw.
Unified thread standards are often used in aircraft, automobiles, and motorcycles, in particular. Unified thread standards are also used in measuring instruments and industrial robots manufactured overseas. They are used in a wide range of locations, including the United Kingdom, the United States, and Canada.
Unified thread standards are also used in some domestic equipment, but that is mostly because the parts to be fastened are manufactured overseas.
The principle of unified thread standards is no different from that of a normal screw. By lifting a heavy object using the screw's slope, the screw body can be pulled even with a small tightening torque, thus generating a large fastening force, or axial force.
The reason why the screw does not slacken when tightened is because of the frictional force on the screw's slope. The frictional force, which is greater than the force of the slope component of gravity, maintains the fastening force without sagging. The screw thread angle, which is the ridge of the screw thread, is 60°, the same as that of a metric screw. The aforementioned Witt screw has a thread angle of 55°.
As with metric screws, there are two types of unified thread standards: coarse and fine. As described below, the UNC is used for the coarse threads and UNF for the fine threads.
The difference between coarse and fine threads is the thread pitch, with fine threads having more peaks lined up on the same shaft length than coarse threads. The finer threads are less likely to loosen due to the finer arrangement of the peaks, but require more turning to tighten. Therefore, it is not suitable for mass production.
Unified thread standards are also represented by letters such as UNC and UNF, as well as fractions. The following is an explanation of how to read the notation with actual examples.
Example: 3/8 - 20UNC x 5/8
1. 3/8: Thread Nominal (thickness)
This indicates the thickness of the screw, including the threads. For inch threads, including a unified thread standard, the number is expressed as a fraction with 8 as the denominator.
2. 20: Number of Screw Threads
This indicates how many thread peaks there are in a length of 1 inch. If the screw is shorter than 1", the number of threads is given as if it were 1" long.
3. UNC: Coarse or Fine
This indicates whether the thread is coarse or fine.
4. 5/8: Length Below the Head of the Screw
This is expressed as a fraction of an inch. The length below the head of the screw is the part of the screw that is below the head of the screw. Since it is the length from the bottom of the neck, it includes the length of the cylindrical part without threads. However, in the case of a screw with a conical head, called a "threaded screw," the total length of the screw corresponds to the length below the neck shown here.
Although the notation is as described above, there are some unique names. First of all, the "thread designation," which indicates the outside diameter of the screw, is written in the form of a number, starting with the thinnest: #0, #1, and #12.
For thicker than #12, the number is indicated by 1/8 or 1/4, which is one inch divided into eight equal parts. Dimensions of threaded parts are also indicated in the same way. And these fractions are also called in a unique way, as follows:
*Including some distributors, etc.
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