Currently, the building materials market often offers pipes whose dimensions are indicated in inches. Many buyers may not pay attention to this, and, therefore, there is a possibility of purchasing a pipe with a size that does not correspond to the required one. The reason for this lies in the fact 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 equal to 25.4 millimeters. This value differs from accepted millimeter standards, which can greatly complicate the selection of the required part.
Inch cylindrical thread provides for the display of 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 inch values, in practice there is a significant difference between the thread sizes on the pipe. This is because Western standards say: inch thread indicates the internal 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 says that the inch thread is ½. Thus, you get a pipe with an outer diameter of 20,95 mm, instead of the expected 12.7 mm. Therefore, the pipe inch is equal to 33.249 mm and consists of the size of the direct passage and twice the wall thickness.
From this example, it can be seen that the use of this indicator is more acceptable, since such a system best characterizes the size that an inch thread has.
Now that the designations have become clear, we can proceed to the classification and purpose of this parameter.
Cylindrical inch thread according to the purpose and nature of the work performed is divided into:
- Mounting thread. This type traditionally includes metric and inch threads, which have a triangular profile. Metric is used in the design of new machines and units, while the second is necessary for the production of various spare parts.
- Special threads include many different non-standard sizes.
Metric threads are often available with a 60° profile. All values, whether thread pitch or outer diameter, are indicated in millimeters.
According to the pitch, one main and 5 types of auxiliary threads are distinguished (it is also called fine). It should be noted that such a thread is considered more durable than a large one (with absolutely equal outer diameters). The undoubted advantage of fine threads can also be called a small helix angle and, as a result, increased resistance to twisting.
Threads of this type are used in the most loaded hollow parts, as well as in elements that are subject to strong shocks and vibrations. The adjusting nuts are also threaded like this as it allows finer adjustments.
In addition, inch threads can be made at 55°. In this case, the diameter is still specified in inches, but the thread pitch is determined by the number of threads per inch. A similar type is used in various threaded connections for mechanically fixing parts together.
