Currently, pipes are often offered on the building materials market in inches. Many buyers may not pay attention to this, and therefore there is a possibility of acquiring a pipe with a size that does not match the required. The reason for this is that the inch thread (designation on the surface of the pipe), as the name implies, is measured in inches. In this case, one inch is 25.4 millimeters. This value differs from the accepted millimeter standards, which can greatly complicate the choice of the necessary part.
An inch cylindrical thread provides for displaying the pipe dimensions in inches, while the thread pitch is indicated in fractions of this unit of measurement (due to its small size).
Due to the discrepancy between the millimeter and the inch, in practice a significant difference appears between the dimensions of the thread on the pipe. This is because Western standards state: inch thread indicates the inner diameter of the pipe. In this case, the differences between the metric inch and the so-called pipe inch should be taken into account.
For example, the pipe indicates that the inch thread has a size of ½. Thus, you get a pipe with an outer diameter of 20.95 mm, instead of the expected 12.7 mm. Consequently, the tube inch is 33.249 mm and consists of the size of the passage itself and the double wall thickness.
This example shows that the use of this indicator is more acceptable, since such a system best describes the size that an inch thread has.
Now that the notation has become clear, we can proceed to the classification and purpose of this parameter.
The cylindrical inch thread for the purpose and nature of the work carried out is divided into:
- Fixing thread. This type is traditionally classified as metric thread and inch, having a triangular profile. Metric is used in the design of new machines and assemblies, while the second is necessary for the production of various spare parts.
- Special threads include many different sizes that do not meet standards.
Metric threads are often available with a profile having an angle of 60 °. All values, whether it is a thread pitch or an outer diameter, are indicated in millimeters.
By the size of the step, one main and 5 types of auxiliary thread are distinguished (it is also called shallow). It should be noted that such a thread is considered more durable than coarse (with absolutely equal outer diameters). The undoubted advantage of small threads can also be called a small angle of elevation of the helix and, as a result, increased twisting resistance.
Threads of this type are used in the most loaded hollow parts, as well as in elements that are subject to strong shocks and shocks. The adjusting nuts also have a similar thread, since it allows for more precise adjustment.
In addition, inch thread can be performed at a rotation angle of 55 °. In this case, the diameter is still set in inches, but the thread pitch is determined by the number of threads per inch. A similar type is used in various threaded joints for mechanically fixing parts together.