Her Majesty the trumpet! Of course, it makes our lives better. Something like this:

The key characteristic of any cylindrical pipe is its diameter. It can be internal ( Du) and external ( Dn). Pipe diameter is measured in millimeters, but the unit of pipe thread is inch.

At the junction of the metric and foreign measurement systems, the most questions usually arise.

Besides, it's real existing size internal diameter often does not coincide with Dy.

Let's take a closer look at how we can continue to live with this. A separate article is devoted to pipe threads. Read also about profile pipes, which are used for the construction of structures.

Inches vs mm. Where does the confusion come from and when is a correspondence table needed?

Pipes whose diameter is indicated in inches ( 1", 2" ) and/or fractions of inches ( 1/2", 3/4" ), are a generally accepted standard in water and water-gas supply.

What's the difficulty?

Take dimensions from the pipe diameter 1" (how to measure pipes is written below) and you will get 33.5 mm, which naturally does not coincide with the classical linear table for converting inches to mm ( 25.4 mm).

As a rule, the installation of inch pipes proceeds without difficulty, but when replacing them with pipes made of plastic, copper and stainless steel, a problem arises - a discrepancy between the size of the designated inch ( 33.5 mm) to his actual size (25.4 mm).

Usually this fact causes bewilderment, but if you look deeper into the processes occurring in the pipe, the logic of the size discrepancy becomes obvious to a layman. It's quite simple - read on.

The fact is that when creating a water flow, the key role is played not by the external, but by the internal diameter, and for this reason it is used for designation.

However, the discrepancy between designated and metric inches still remains, since the internal diameter of a standard pipe is 27.1 mm, and reinforced - 25.5 mm. The last value is quite close to equality 1""=25,4 but still he is not.

The solution is that to designate the size of pipes, a nominal diameter rounded to a standard value is used (nominal bore Dy). The nominal diameter is selected so that throughput pipeline increased from 40 to 60% depending on the growth of the index value.

Example:

The outer diameter of the pipe system is 159 mm, pipe wall thickness 7 mm. The exact inner diameter will be D = 159 - 7*2= 145 mm. With wall thickness 5 mm size will be 149 mm. However, in both the first and second cases the conditional passage will have one nominal size 150 mm.

In situations with plastic pipes To solve the problem of inappropriate dimensions, transition elements are used. If it is necessary to replace or connect inch pipes with pipes made according to real metric dimensions - copper, stainless steel, aluminum, both the outer and inner diameters should be taken into account.

Table of nominal diameter in inches

Du	Inches	Du	Inches	Du	Inches
6	1/8"	150	6"	900	36"
8	1/4"	175	7"	1000	40"
10	3/8"	200	8"	1050	42"
15	1/2"	225	9"	1100	44"
20	3/4"	250	10"	1200	48"
25	1"	275	11"	1300	52"
32	1(1/4)"	300	12"	1400	56"
40	1(1/2)"	350	14"	1500	60"
50	2"	400	16"	1600	64"
65	2(1/2)"	450	18"	1700	68"
80	3"	500	20"	1800	72"
90	3(1/2)"	600	24"	1900	76"
100	4"	700	28"	2000	80"
125	5"	800	32"	2200	88"

Table. Inner and outer diameters. Stacked water/water-gas pipelines, epectros-welded longitudinal, seamless hot-deformed steel and polymer pipes

Table of correspondence between nominal diameter, thread and outer diameters of the pipeline in inches and mm.

Nominal pipe diameter Dy. mm	Thread diameter G". inch	Pipe outer diameter Dn. mm
		Water/water-gas pipes GOST 3263-75	Epoxy-welded straight-seam steel pipes GOST 10704-91. Seamless hot-deformed steel pipes GOST 8732-78. GOST 8731-74 (FROM 20 TO 530 ml)	Polymer pipe. PE, PP, PVC

GOST- state standard used in heat - gas - oil - pipelines

ISO- standard for designating diameters, used in plumbing engineering systems

SMS- Swedish standard for pipe diameters and valves

DIN/EN- the main European range for steel pipes according to DIN2448 / DIN2458

DU (Dy)- conditional passage

Size tables polypropylene pipes presented in the next article >>>

Conformity table for nominal pipe diameters with international markings

GOST	ISO inch	ISO mm	SMS mm	DIN mm	DU
8	1/8	10,30			5
10	1/4	13,70	6,35		8
12	3/8	17,20	9,54	12,00	10
18	1/2	21,30	12,70	18,00	15
25	3/4	26,90	19,05	23(23)	20
32	1	33,70	25,00	28,00	25
38	1 ¼	42,40	31,75	34(35)	32
45	1 ½	48,30	38,00	40,43	40
57	2	60,30	50,80	52,53	50
76	2 ½	76,10	63,50	70,00	65
89	3	88,90	76,10	84,85	80
108	4	114,30	101,60	104,00	100
133	5	139,70	129,00	129,00	125
159	6	168,30	154,00	154,00	150
219	8	219,00	204,00	204,00	200
273	10	273,00	254,00	254,00	250

Diameters and other characteristics of stainless steel pipes

Passage, mm	Diameter outer, mm	Wall thickness, mm		Weight of 1 m pipe (kg)
		standard	reinforced	standard	reinforced
10	17	2.2	2.8	0.61	0.74
15	21.3	2.8	3.2	1.28	1.43
20	26.8	2.8	3.2	1.66	1.86
25	33.5	3.2	4	2.39	2.91
32	42.3	3.2	4	3.09	3.78
40	48	3.5	4	3.84	4.34
50	60	3.5	4.5	4.88	6.16
65	75.5	4	4.5	7.05	7.88
80	88.5	4	4.5	8.34	9.32
100	114	4.5	5	12.15	13.44
125	140	4.5	5.5	15.04	18.24
150	165	4.5	5.5	17.81	21.63

Did you know?

What ingenious lamps can you assemble with your own hands from ordinary metal pipe? Anyone can do this!

Which pipe is considered small - medium - large?

Even in serious sources, I have seen phrases like: “We take any pipe of average diameter and...”, but no one indicates what this average diameter is.

To figure it out, you should first understand what diameter you need to focus on: it can be internal or external. The first is important when calculating the transport capacity of water or gas, and the second is important for determining the ability to withstand mechanical loads.

External diameters:

From 426 mm is considered large;

102-246 is called average;

5-102 is classified as small.

As for the internal diameter, it is better to look at the special table (see above).

How to find out the diameter of a pipe? Measure!

For some reason this strange question often comes to e-mail and I decided to supplement the material with a paragraph about measurement.

In most cases, when purchasing, it is enough to look at the label or ask the seller a question. But it happens that you need to repair one of the communication systems by replacing pipes, and initially it is not known what diameter the already installed ones have.

There are several ways to determine the diameter, but we will list only the simplest ones:

Arm yourself with a tape measure or a measuring tape (this is how women measure their waist). Wrap it around the pipe and record the measurement. Now, to obtain the desired characteristic, it is enough to divide the resulting figure by 3.1415 - this is the number Pi.

Example:

Let's imagine that the girth (circumference L) of your pipe is 59.2 mm. L=ΠD, resp. the diameter will be: 59.2 / 3.1415= 18.85 mm.

• After obtaining the outer diameter, you can find out the inner one. Only for this you need to know the thickness of the walls (if there is a cut, just measure with a tape measure or other device with a millimeter scale).

  Let's assume that the wall thickness is 1 mm. This figure is multiplied by 2 (if the thickness is 3 mm, then it is also multiplied by 2 in any case) and subtracted from the outer diameter (18.85- (2 x 1 mm) = 16.85 mm).

  It’s great if you have a caliper at home. The pipe is simply grabbed by the measuring teeth. We look at the required value on a double scale.

Types of steel pipes according to their production method

Electric welded (straight seam)

For their manufacture, strips or sheet steel are used, which are bent into shape using special equipment. required diameter, and then the ends are connected by welding.

The effect of electric welding guarantees a minimum seam width, which makes it possible to use them for the construction of gas or water pipelines. The metal is in most cases carbon or low alloy.

Indicators finished products are regulated by the following documents: GOST 10704-91, GOST 10705-80 GOST 10706-76.

Please note that a pipe manufactured in accordance with standard 10706-26 is distinguished by maximum strength among its peers - after creating the first connecting seam, it is strengthened by four additional ones (2 inside and 2 outside).

IN regulatory documentation The diameters of products produced by electric welding are indicated. Their size ranges from 10 to 1420 mm.

Spiral seam

The material for production is steel in rolls. The product is also characterized by the presence of a seam, but unlike the previous production method, it is wider, which means the ability to withstand high internal pressure is lower. Therefore, they are not used for the construction of gas pipeline systems.

A specific type of pipe is regulated by GOST number 8696-74 .

Seamless

The production of a specific type involves the deformation of specially prepared steel blanks. The deformation process can be carried out both under the influence high temperatures, and cold method (GOST 8732-78, 8731-74 and GOST 8734-75, respectively).

The absence of a seam has a positive effect on the strength characteristics - the internal pressure is evenly distributed over the walls (there are no “weak” places).

As for diameters, standards control their production with a value of up to 250 mm. When purchasing products with sizes exceeding those indicated, you have to rely only on the integrity of the manufacturer.

Important to know!

If you want to buy the most durable material, buy seamless cold-formed pipes. The absence of temperature influences has a positive effect on preserving the original characteristics of the metal.

Also if important indicator is the ability to withstand internal pressure, then choose round products. Profile pipes cope better with mechanical loads (they are well made from metal frames etc.).

Here are a couple more excellent slides of creative advertising for a pipe manufacturer:

On construction market 2 sizes of designs are popular:

• 1\2 and 3\4 – make up separate category. due to special thread parameters (1.814), per 1 unit. measures account for 14 threads;
• within 1 - 6 inches, the pitch is reduced to 2.309, forming 11 threads, which does not affect the reduction or improvement of the quality of the connection.

One inch is 25.4 mm long, it is used to determine the internal parameters, but when laying reinforced pipes, the diameter is 33.249 mm (including the internal section and 2 walls). In assortment steel structures there is an exception - ½ inch products, where the outer section is 21.25 mm. This parameter is used when calculating the dimensions of pipes with cylindrical threads. When making calculations for pipes with a cross section of 5 inches, the internal dimension will be 12.7 cm, and the external dimension will be 166.245 (reduction to 1 decimal place is allowed).

Difference between measurement systems

In terms of external parameters, inch designs do not differ from metric ones, the difference lies in the type of notches. There are 2 types of threads according to the inch system - English and American. The first option corresponds to a notch angle of 55 degrees, and the metric (American) system with an angle of 60 degrees. generally accepted.

At different degrees, it is difficult to distinguish between an angle of 55 for inch and 60 for metric designs, and the rounding of the threads is immediately visible, making it impossible for an error to occur. To measure the thread pitch, a thread gauge is used, but instead of it, a regular ruler or other device can be used well.

Replacing steel pipes with polymer ones

In the gas and water supply networks, steel products are used, the diameter of which is indicated in inches (1", 2") or fractions (1/2", 3/4"). When measuring the cross-section of a 1" pipe, the result will be 33.5 mm, which corresponds to 1" (25.4 mm). When arranging pipeline reinforcing elements, where the parameters are indicated in inches, no difficulties arise. But when installing products made of PP, copper or stainless steel instead of steel structures, it is necessary to take into account the difference in name and parameters.

To create a given flow level, the internal diameter of the pipes is taken into account. For ordinary inch pipes it is 27.1 mm, for reinforced pipes it is 25.5 mm, closest to 1". Pipelines are designated in conventional units of the flow area Du (DN). It determines the parameters of the lumen of pipes and is designated in digital values. The pitch of the nominal flow section is selected taking into account the increase in flow characteristics by 40-60% with an increase in the index. If the external cross-section and purpose of the structures are known, using a size table, the internal cross-section is determined.

In the process of connecting steel pipes with polymer structures, replacing one with another, conventional adapters are used. Dimensional discrepancies result from the use of copper, aluminum or stainless steel products manufactured to metric standards. The actual metric dimensions of the pipes are taken into account - internal and external.

Steel pipes of the Russian Federation in comparison with the European standard

To compare the range of pipes according to GOST of the Russian Federation and European standards, the following table is used:

How to decide on the diameter?

From diameter water pipes their throughput characteristics depend - the volume of water passed per 1 unit. time. It depends on the speed of water flow. As it increases, the risk of pressure drop in the line increases. Flow characteristics are calculated using formulas, but when planning intra-apartment wiring, they take pipes of certain parameters.

For the plumbing system:

• 1.5 cm (1/2 inch)
• 1 cm (3/8 inch).

For the riser, structures with an internal cross section are used:

• 2.5 cm (1 inch);
• 2 cm (3/4 inch).

Taking into account the fact that the internal cross-section of half-inch polymer pipes varies from 11 to 13 mm, and one-inch ones - from 21 to 23, an experienced plumber will be able to determine the exact parameters when replacing. With a complex type of wiring, numerous joints, turns and network laying on long distance, reducing pressure, it is necessary to provide for the possibility of routing pipes with a large cross-section. As the diameter increases, the pressure level increases.

Below is a table for determining the permeability of steel pipes:

Steel pipe diameter

The cross-section of the pipes corresponds to a number of indicators:

• Nominal diameter (DN, Dy) – nominal parameters (in mm) of the internal cross-section of pipes or their rounded values, in inches.
• Nominal parameter (Dn Dn,).
• External size.

  The metric calculation system allows you to classify structures into small - from 5...102 mm, medium - from 102...426, large - 426 mm and more.

• Wall thickness.
• Inner diameter.

The internal cross-section of pipes with different threads corresponds to the following parameters:

• 1/2 inch pipeline - 1.27 cm;
• 3/4 inch – 1.9 cm;
• 7/8 inches - 2.22 cm;
• 1 inch – 2.54 cm;
• 1.5 inches - 3.81 cm;
• 2 inches - 5.08 cm.

To determine the thread diameter, the following indicators are used:

• 1/2 inch pipeline – 2.04 - 2.07 cm;
• 3/4 inches – 2.59 - 2.62 cm;
• 7/8 inches – 2.99 - 3 cm;
• 1 inch – 3.27 - 3.3 cm;
• 1.5 inches - 4.58 - 4.62 cm;
• 2 inches – 5.79 - 5.83 cm.

Table of correspondence between the diameter of steel pipes and polymer structures:

Steel pipe prices:

PP pipe diameter

PP pipes are produced with a diameter from 0.5 to 40 cm or more. The diameter is internal and external. The first indicator allows you to find out the volume of media passed through in 1 unit. time. The external cross-section is used to carry out construction calculations, namely the selection of a niche or hole for laying a highway. External parameters allow you to choose the right fittings with the corresponding internal indicators.

• Small – 0.5; 1; 1.5; 2; 2.5; 3.2; 4; 5; 6.3 and 7.5 cm are used for heating systems, drainage and water supply in private buildings. An internal cross section of 3.2 cm is most popular in multi-story buildings.
• Average – 8; 9; 10; 11; 12.5; 16; 20; 25 and 31.5 cm are used for arranging water supply and sewer systems, allowing you to change cast iron products with similar external parameters. Inner size in 8, 9 and 10 cm ideal for chemical media.
• Large - 40 cm or more is used for arranging cold water supply and ventilation systems.

Pipes are marked in inches and mm. When choosing designs for plumbing and heating system, the wall thickness is taken into account, affecting the conditional passability of highways with the same external parameters. With an increase in its parameter, an increase in pressure in the water supply system is allowed. Small dimensions allow you to reduce the cost of purchasing material and water consumption.

Cost of PP pipes:

Video

This article will discuss concepts related to threaded connections such as metric and inch threads. To understand the intricacies associated with a threaded connection, it is necessary to consider the following concepts:

Tapered and cylindrical threads

The rod itself with tapered thread is a cone. Moreover, according to international rules, the taper should be 1 to 16, that is, for every 16 units of measurement (millimeters or inches) with increasing distance from the starting point, the diameter increases by 1 corresponding unit of measurement. It turns out that the axis around which the thread is applied and the conditional straight line drawn from the beginning of the thread to its end along the shortest path are not parallel, but are located at a certain angle to each other. To explain it even more simply, if we had a threaded connection length of 16 centimeters, and the diameter of the rod at its starting point was 4 centimeters, then at the point where the thread ends, its diameter would already be 5 centimeters.

Rod with cylindrical thread is a cylinder, therefore there is no taper.

Thread pitch (metric and inch)

The thread pitch can be large (or main) and small. Under thread pitch refers to the distance between the threads from the top of the thread to the top of the next thread. You can even measure it using a caliper (although there are also special meters). This is done as follows - the distance between several tops of the turns is measured, and then the resulting number is divided by their number. You can check the measurement accuracy using the table for the corresponding step.

Cylindrical pipe thread according to GOST 6357-52
Designation	Number of threads N by 1"	Thread pitch S, mm	O.D thread, mm	Average diameter thread, mm	Inner diameter thread, mm
G1/8"	28	0,907	9,729	9,148	8,567
G1/4"	19	1,337	13,158	12,302	11,446
G3/8"	19	1,337	16,663	15,807	14,951
G1/2"	14	1,814	20,956	19,754	18,632
G3/4"	14	1,814	26,442	25,281	24,119
G7/8"	14	1,814	30,202	29,040	27,878
G1"	11	2,309	33,250	31,771	30,292

Nominal thread diameter

The labeling usually contains nominal diameter, which in most cases is taken to be O.D. thread. If the thread is metric, then you can use a regular caliper with scales in millimeters to measure. Also, the diameter, as well as the thread pitch, can be viewed using special tables.

Metric and inch threads with examples

Metric thread– has the designation of the main parameters in millimeters. For example, consider an elbow fitting with an external cylindrical thread. EPL 6-GM5. IN in this case EPL says that the fitting is angled, 6 is 6 mm - the outer diameter of the tube connected to the fitting. The letter “G” in its marking indicates that the thread is cylindrical. “M” indicates that the thread is metric, and the number “5” indicates the nominal diameter of the thread, equal to 5 millimeters. Fittings (from those we have on sale) with the letter “G” are also equipped with a rubber o-ring, and therefore do not require fum tape. The thread pitch in this case is 0.8 millimeters.

Basic parameters inch thread , according to the name, are indicated in inches. This can be a 1/8, 1/4, 3/8 and 1/2 inch thread, etc. For example, let's take a fitting EPKB 8-02. EPKB is a type of fitting (in this case a splitter). The thread is conical, although there is no reference to this using the letter “R”, which would be more correct. 8 - indicates that the outer diameter of the connected tube is 8 millimeters. A 02 - that the connecting thread on the fitting is 1/4 inch. According to the table, the thread pitch is 1.337 mm. The nominal thread diameter is 13.157 mm.

The profiles of the conical and cylindrical threads coincide, which allows fittings with conical and cylindrical threads to be screwed together.

This article will discuss concepts related to threaded connections such as metric and inch threads. To understand the intricacies associated with a threaded connection, it is necessary to consider the following concepts:

Tapered and cylindrical threads

The rod itself with tapered thread is a cone. Moreover, according to international rules, the taper should be 1 to 16, that is, for every 16 units of measurement (millimeters or inches) with increasing distance from the starting point, the diameter increases by 1 corresponding unit of measurement. It turns out that the axis around which the thread is applied and the conditional straight line drawn from the beginning of the thread to its end along the shortest path are not parallel, but are located at a certain angle to each other. To explain it even more simply, if we had a threaded connection length of 16 centimeters, and the diameter of the rod at its starting point was 4 centimeters, then at the point where the thread ends, its diameter would already be 5 centimeters.

Rod with cylindrical thread is a cylinder, therefore there is no taper.

Thread pitch (metric and inch)

The thread pitch can be large (or main) and small. Under thread pitch refers to the distance between the threads from the top of the thread to the top of the next thread. You can even measure it using a caliper (although there are also special meters). This is done as follows - the distance between several tops of the turns is measured, and then the resulting number is divided by their number. You can check the measurement accuracy using the table for the corresponding step.

Cylindrical pipe thread according to GOST 6357-52
Designation	Number of threads N by 1"	Thread pitch S, mm	O.D thread, mm	Average diameter thread, mm	Inner diameter thread, mm
G1/8"	28	0,907	9,729	9,148	8,567
G1/4"	19	1,337	13,158	12,302	11,446
G3/8"	19	1,337	16,663	15,807	14,951
G1/2"	14	1,814	20,956	19,754	18,632
G3/4"	14	1,814	26,442	25,281	24,119
G7/8"	14	1,814	30,202	29,040	27,878
G1"	11	2,309	33,250	31,771	30,292

Nominal thread diameter

The labeling usually contains nominal diameter, which in most cases is taken to be the outer diameter of the thread. If the thread is metric, then you can use a regular caliper with scales in millimeters to measure. Also, the diameter, as well as the thread pitch, can be viewed using special tables.

Metric and inch threads with examples

Metric thread– has the designation of the main parameters in millimeters. For example, consider an elbow fitting with an external cylindrical thread. EPL 6-GM5. In this case, EPL says that the fitting is angled, 6 is 6 mm - the outer diameter of the tube connected to the fitting. The letter “G” in its marking indicates that the thread is cylindrical. “M” indicates that the thread is metric, and the number “5” indicates the nominal diameter of the thread, equal to 5 millimeters. Fittings (of those that we have on sale) with the letter “G” are also equipped with a rubber O-ring, and therefore do not require fumigation tape. The thread pitch in this case is 0.8 millimeters.

Basic parameters inch thread, according to the name, are indicated in inches. This can be a 1/8, 1/4, 3/8 and 1/2 inch thread, etc. For example, let's take a fitting EPKB 8-02. EPKB is a type of fitting (in this case a splitter). The thread is conical, although there is no reference to this using the letter “R”, which would be more correct. 8 - indicates that the outer diameter of the connected tube is 8 millimeters. A 02 - that the connecting thread on the fitting is 1/4 inch. According to the table, the thread pitch is 1.337 mm. The nominal thread diameter is 13.157 mm.

The profiles of the conical and cylindrical threads coincide, which allows fittings with conical and cylindrical threads to be screwed together.

Inch threads are used primarily to create pipe connections: they are applied both to the pipes themselves and to metal and plastic fittings necessary for the installation of pipe lines for various purposes. The main parameters and characteristics of the threaded elements of such connections are regulated by the corresponding GOST, providing tables of inch thread sizes, which experts rely on.

Basic parameters

The regulatory document that stipulates the requirements for the dimensions of cylindrical inch threads is GOST 6111-52. Like any other, inch thread is characterized by two main parameters: pitch and diameter. The latter usually means:

• outer diameter measured between the top points of the threaded ridges located on opposite sides pipes;
• internal diameter as a value characterizing the distance from one lowest point of the cavity between the threaded ridges to another, also located on opposite sides of the pipe.

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

The second important parameter - the pitch - characterizes the distance at which two adjacent ridges or two adjacent depressions are located from each other. Throughout the entire area of ​​the product where the pipe thread, its step does not change and has the same value. If so important requirement will not be observed, it will simply not work, it will not be possible to select the second element of the created connection for it.

You can familiarize yourself with the provisions of GOST regarding inch threads by downloading the document in pdf format follow the link below.

Table of sizes of inch and metric threads

Learn how metric threads relate to various types inch threads, you can use the data from the table below.

Similar sizes metric and different varieties inch threads in the range of approximately Ø8-64mm

Differences from metric threads

According to their own external signs and characteristics, metric and inch threads do not have many differences, the most significant of which include:

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

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

The 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 the latter, respectively, in inches. However, it should be borne in mind that in relation to an inch thread, it is not the generally accepted one (2.54 cm), but a special pipe inch equal to 3.324 cm that is used. Thus, if, for example, its diameter is ¾ inch, 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, just look at the special table. The tables containing inch thread sizes contain both whole and fractional values. It should be borne in mind that the pitch in such tables is given in the number of cut grooves (threads) contained in one inch of product length.

To check whether the pitch of the thread already made corresponds to the dimensions specified by GOST, this parameter must be measured. For such measurements, carried out for both metric and inch threads using the same algorithm, standard tools are used - a comb, gauge, mechanical gauge, etc.

The easiest way to measure the pitch of an inch pipe thread is using the following method:

• As a simple template, a coupling or fitting is used, the internal thread parameters of which exactly correspond to the requirements given by GOST.
• Bolt, parameters external thread which needs to be measured is screwed into the coupling or fitting.
• In the event that the bolt has formed a tight connection with the coupling or fitting threaded connection, then the diameter and pitch of the thread that is applied to its surface exactly correspond to the parameters of the template used.

If the bolt does not screw into the template or screws in but creates a loose connection with it, then such measurements should be carried out using another coupling or another fitting. The internal pipe thread is measured using a similar technique, only in such cases a product with an external thread is used as a template.

The required dimensions can be determined using a thread gauge, which is a plate with notches, the shape and other characteristics of which exactly correspond to the parameters of the thread with a certain pitch. Such a plate, acting as a template, is simply applied to the thread being checked with its serrated part. The fact that the thread on the element being tested corresponds to the required parameters will be indicated by a tight fit of the jagged part of the plate to its profile.

To measure the outside diameter of an inch or metric thread, you can use a regular caliper or micrometer.

Slicing technologies

Cylindrical pipe threads, which are of the inch type (both internal and external), can be cut manually or mechanical method.

Manual thread cutting

Thread cutting using hand tools, which uses a tap (for internal) or a die (for external), is performed in several steps.

1. The pipe being processed is clamped in a vice, and the tool used is fixed in a driver (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 inside of the latter.
3. The tool used is screwed into the pipe or screwed onto its end by rotating a driver or die holder.
4. To make the result cleaner and more precise, you can repeat the cutting procedure several times.

Thread cutting on a lathe

Mechanically, pipe threads are cut according to the following algorithm:

1. The pipe being processed is clamped in the machine chuck, on the support of which a thread-cutting tool is fixed.
2. At the end of the pipe, using a cutter, a chamfer is removed, after which the speed of movement of the caliper is adjusted.
3. After bringing the cutter to the surface of the pipe, the machine turns on the threaded feed.

It should be borne in mind that inch threads are cut mechanically using lathe only on tubular products whose thickness and rigidity allow this to be done. Making pipe inch threads mechanically allows you to obtain high-quality results, but the use of such technology requires the turner to have appropriate qualifications and certain skills.

Accuracy classes and marking rules

A thread belonging to the inch type, as indicated by GOST, can correspond to one of three accuracy classes - 1, 2 and 3. Next to the number indicating 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 class 1 corresponds to the coarsest threads, and class 3 corresponds to the most precise threads, the dimensions of which are subject to very stringent requirements.