Inch thread is mainly used to create pipe connections: it is applied as on the pipes themselves, as well as for metal and plastic fittings, necessary for the installation of pipelines for various purposes. The main parameters and characteristics of threaded elements of such compounds are regulated by the corresponding GOST, giving tables of inch thread sizes, on which specialists are oriented.

Plumbing products with pipe inch thread

MAIN PARAMETERS

Regulatory document, which stipulates the requirements for the dimensions of the cylindrical inch thread, there is GOST 6111-52. Like any other, inch thread is characterized by two main parameters: step and diameter. The latter is usually understood:

• outer diameter, measured between the upper points of the threaded ridges, located on opposite sides of the pipe;
• inner diameter as a value, which characterizes the distance from the lowest point of the depression between the threaded ridges to the other, are also on opposite sides of the pipe.

Knowing the outer and inner diameters of the inch thread, you can easily calculate the height of her profile. To calculate this size, it is enough to determine the difference between these diameters.

The second important parameter - step - characterizes, at what distance from each other are two adjacent ridges or two adjacent depressions. On the entire area of ​​the product, on which the pipe thread is made, its step does not change and has the same value. If such an important requirement is not met, she will simply be idle, it will not be possible to match the second element of the created connection to it.

You can familiarize yourself with the provisions of GOST regarding inch threads, by downloading the document in pdf format at the link below.
GUEST 6111-52 Inch conical thread with a profile angle of 60°
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TABLE OF DIMENSIONS OF INCHES AND METRIC THREADS

Learn, how metric threads relate to different types of inch threads, you can using the data from the table below.

Similar sizes of metric and various varieties of inch threads in the range of approximately O8-64mm

DIFFERENCES FROM METRIC THREAD

According to their external features and characteristics, metric and inch threads do not have many differences, among the most significant of which it is worth mentioning:

• the shape of the threaded profile of the comb;
• the procedure for calculating the diameter and pitch.

When comparing the shapes of the threaded combs, you can see, that such elements are sharper in the inch thread, than in metric. If we talk about the exact dimensions, then the angle at the top of the inch thread crest is 55°.

Parameters of metric and inch threads are characterized by different units of measurement. So, the diameter and pitch of the former are measured in millimeters, and others, in accordance, in inches. Trace, however, to mean, that in relation to the inch thread is not generally used (2,54 cm), and the special pipe inch is equal 3,324 div. So, if, example, its diameter is ? in, then in terms of millimeters it will correspond to the value 25.

To find out the basic parameters of an inch thread of any standard size, which is fixed by GOST, it is enough to look at the special table. In the tables, containing inch thread sizes, are given as targets, and fractional values. It should be borne in mind, that the step in such tables is given in the number of cut grooves (thread), contained in one inch of product length.

To check, does the step of the already made carving correspond to the dimensions, which are determined by GOST, this parameter must be measured. For such measurements, which are conducted as for metric, as well as for inch threads according to one algorithm, standard tools are used - a comb, caliber, mechanical meter, etc.

The easiest way to measure the pitch of a pipe inch thread is with the following technique:

• A coupling or fitting is used as the simplest template, parameters of the internal thread of which exactly meet the requirements, which provides GOST.
• Bolt, the parameters of the external thread of which must be measured, is screwed into the coupling or fitting.
• In that case, if the bolt has formed a tight threaded connection with the coupling or fitting, diameter and pitch of the thread, which is applied to its surface, exactly match the parameters of the template.

Inch thread pitch is the number of turns per inch

If the screw does not screw into the template or is screwed, but creates a loose connection with it, then the following measurements should be made, using a different coupling or a different fitting. The internal pipe thread is measured by a similar method, only as a template in such cases, a product with an external thread is used.

You can determine the required dimensions using a thread gauge, which is a plate with slits, the shape and other characteristics of which exactly correspond to the parameters of the thread with a certain pitch. Such a plate, which acts as a template, simply applied to the tested thread with its serrated part. About that, that the carving on the human element meets the necessary parameters, will show a tight fit to its profile with a jagged part of the plate.

In order to measure the size of the outer diameter of an inch or metric thread, a regular caliper or micrometer can be used.

CUTTING TECHNOLOGIES

Cylindrical tube thread, which refers to the inch type (as internal, and external), can be cut manually or mechanically.

Manual thread cutting

Threading with a hand tool, as which a tap is used (for internal) or a die (for external), performed in several steps.

1. The processed pipe is clamped in a vise, and the used tool is fixed in the handle (tap) or in a die holder (die).
2. The die is put on the end of the pipe, and the tap is inserted into the inner part of the latter.
3. The tool used is screwed into the pipe or screwed onto its end by rotating the drill bit or die holder.
4. To make the result more clean and accurate, you can repeat the cutting procedure several times.

The pipe thread is mechanically cut according to the following algorithm:

1. The processed pipe is clamped in the chuck of the machine, on the caliper of which the threaded cutter is fixed.
2. At the end of the pipe, using a cutter, remove the chamfer, after that, adjust the caliper movement speed.
3. After bringing the cutter to the surface of the pipe, the threading feed is included on the machine.

It should be borne in mind, that the inch thread is cut by a mechanical method using a lathe only on pipe products, the thickness and rigidity of which allow it to be done. Performing pipe inch threading by a mechanical method allows you to get a high-quality result, but the use of such technology requires the turner to have appropriate qualifications and certain skills.

ACCURACY CLASSES AND MARKING RULES

Carving, which refers to the inch type, as indicated by GOST, can correspond to one of three classes of accuracy - 1, 2 and 3. Next to the number, which indicates the accuracy class, put the letters "A" (external) or "B" (internal). The full designations of thread accuracy classes, depending on its type, look like 1A, 2A and 3A (for external) and 1B, 2B and 3B (for internal). It should be borne in mind, that the roughest threads correspond to the 1st class, and on the 3rd - the most accurate, the dimensions of which are subject to very strict requirements.

To understand, which parameters a specific threaded element corresponds to, it is enough to understand the marking of the thread, which is applied to it. Marking, which is in question, used by many foreign manufacturers, which work according to American standards, belong to the elements of threaded connections.

This marking contains the following information about the thread:

• nominal size (outer diameter) - the first digits;
• number of turns, which is per inch of length;
• group;
• accuracy class.

The letters LH may also be present in the inch thread designation, which indicate that, that her twists have no right, and the left is the direction.