Her Majesty the trumpet! Of course, it makes our lives better. Like that:

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, installation of inch pipes occurs without difficulties, but when replacing them with pipes made of plastic, copper and of stainless steel a problem arises - the size of the designated inch does not match ( 33.5 mm) to its 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 indicate the size of pipes, a nominal value is used, rounded to standard value diameter (nominal diameter Dy). The size of the nominal diameter is selected so that the throughput of the pipeline increases from 40 to 60% depending on the growth of the index value.

Example:

Outside diameter pipe system is equal to 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 the same nominal size 150 mm.

In situations with plastic pipes To solve the problem of inappropriate dimensions, transition elements are used. If necessary, replace or connect inch pipes with pipes made according to real metric sizes- made of copper, stainless steel, aluminum, both 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 pass

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 measuring tape(women measure their waist this way). 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. Required value look at the 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

Production 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.

It is important to know!

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

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

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

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 size tables inch thread, which experts focus on.

Main settings

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 top points threaded ridges located on opposite sides of the pipe;
• 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.

Second important parameter– step – 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 such an important requirement is not met, it will simply not work; it will not be possible to select a second element of the connection being created for it.

Familiarize yourself with the provisions of GOST regarding inch threads You can download the document in pdf format from 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 speak about exact dimensions, then the angle at the top of the inch thread crest 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. It should, however, 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, a gauge, a mechanical gauge, etc.

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

• As a simple template, use a coupling or fitting, parameters internal thread 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 mechanically.

Manual threading

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 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

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.

Very often on the packaging (box) with a mixer, in the list of product characteristics, you can see the number 3/8 inch in the “connecting size” column.

What size is this, and how will we connect the mixer if we purchase it?

Connecting size is 3/8 inch, corresponds to M10 metric thread. These are the dimensions of the threaded connection of the fitting part of the flexible liner. On one side of such a hose, covered in a metal braid, there is a 10 or 11 millimeter turnkey fitting and a thread at the end of 10 millimeters, or 9.5 millimeters, which corresponds to three-eighths of an inch.

This is what they look like.

First, a short fitting is screwed to the mixer, then a long one. This is so that the edges of the fittings and the thickening of the crimping do not interfere with each other.

Eat Alternative option for reinforced flexible connections these are bellows hoses for mixers. They are not much more expensive, but their service life is many times greater than the service life of a braided rubber hose. So if it's normal flexible liner serves 3-4 years, then bellows up to 10 years.

At the second end, the flexible hose may have a thread instead of a nut, complete with faucets, most often there is a nut, so be aware that if there is a nut at the outlet of your pipeline, you will need to purchase a nipple -