Connection size g1 2. BSP (BSPP) cylindrical pipe thread. Metric and inch threads in examples

This article will discuss concepts related to threaded connections such as metric and inch thread... To understand the intricacies associated with a threaded connection, you need to consider the following concepts:

Tapered and cylindrical threads

The rod itself with applied to it tapered thread is a cone. Moreover, according to international rules, the taper should be 1 to 16, that is, for every 16 units (millimeters or inches) as the distance from the starting point increases, the diameter increases by 1 corresponding unit. It turns out that the axis around which the thread is drawn and the conditional straight line drawn from the beginning of the thread to its end along the shortest path are not parallel, but are at a certain angle to each other. To explain it even easier, if we had a length threaded connection was 16 centimeters, and the diameter of the rod at its starting point would be 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 basic) and small. Under thread pitch the distance between the threads from the top of the thread to the top of the next thread is understood. You can even measure it with a caliper (although there are also special meters). This is done as follows - the distance between several vertices 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	Outside diameter 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 marking usually contains nominal diameter, which in most cases is taken outside diameter carving. If the thread is metric, then a conventional caliper with scales in millimeters can be used for measurement. Also, the diameter, as well as the thread pitch, can be viewed in special tables.

Metric and inch threads in examples

Metric thread- has the designation of the main parameters in millimeters. As an example, consider an elbow fitting with an external straight 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 we have on sale) with the letter "G" are also equipped with a rubber sealing ring, and therefore do not require fum tapes. The thread pitch in this case is 0.8 millimeters.

main parameters inch thread, according to the name - are indicated in inches. This can be 1/8, 1/4, 3/8 and 1/2 inch threads, 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 tapered, although there is no reference to this with the letter "R", which would be more literate. 8 - indicates that the outer diameter of the connected tube is 8 millimeters. And 02 - that the connecting thread on the fitting is 1/4 inch. According to the table, the pitch is 1.337 mm. The nominal thread diameter is 13.157 mm.

The profiles of the tapered and cylindrical threads are the same, which allows you to screw together fittings with tapered and cylindrical threads.

In this article, I want not only to give dry facts about the dimensions of an inch pipe thread with references to standards and GOSTs, but to bring to the reader an interesting fact about the designation features of the latter.

So, those who have already encountered pipe threads were more than once surprised at the discrepancy between the outer diameter of the thread and its designation. For example, a 1/2 inch thread has an outer diameter of 20.95 mm, although logically with metric threads it should be 12.7 mm. The thing is that in the inch thread, the bore of the pipe is actually indicated, and not the outer diameter of the thread. At the same time, adding the pipe wall to the size of the hole, we get an overestimated outer diameter to which we are accustomed to in the notation of metric threads. Conventionally, the so-called pipe inch is 33.249 mm, that is, 25.4 + 3.92 + 3.92 (where 25.4 is the passage, 3.92 is the pipe wall). The pipe walls are taken based on the working pressure for the thread. Depending on the diameter, the pipes also increase accordingly, since a pipe with a large diameter must have thicker walls than a pipe with a smaller dimater for the same working pressure.

Pipe threads are classified as follows:

Cylindrical pipe thread

This is an inch thread based on BSW (British Standard Whitworth) thread and corresponds to BSP (British standard pipe thread) thread, with four pitches of 28,19,14,11 threads per inch. It is cut into pipes up to size 6 ", pipes over 6" are welded.

The angle of the profile at the apex is 55 °, the theoretical height of the profile is H = 0.960491P.

Standards:
GOST 6357-81: Basic standards of interchangeability.
Cylindrical pipe thread. ISO R228, EN 10226, DIN 259, BS 2779, JIS B 0202.

Symbol: letter G, numerical value nominal pipe size in inches (inch), accuracy class of average diameter (A, B), and letters LH for left-hand threads. For example, a thread with a nominal diameter of 1 1/4 ", accuracy class A is designated as G1 1/4-A. Again, it should be borne in mind that the nominal size of the thread corresponds to the pipe clearance in inches. The outer diameter of the pipe is in some proportion with this size and more, respectively, by the thickness of the pipe walls.

Designation of the size of the pipe thread (G), steps and nominal values of the outer, middle and inner thread diameters, mm

Thread size designation		Step P	Thread diameters
Row 1	Row 2	Step P	d = D	d 2 = D 2	d 1 = D 1
1/16"		0,907	7,723	7,142	6,561
1/8"		0,907	9,728	9,147	8,566
1/4"		1,337	13,157	12,301	11,445
3/8"		1,337	16,662	15,806	14,950
1/2"		1,814	20,955	19,793	18,631
	5/8"		22,911	21,749	20,587
3/4"			26,441	25,279	24,117
	7/8"		30,201	29.0З9	27,877
1"		2,309	33,249	31,770	30,291
	1⅛"		37,897	36,418	34,939
1¼ "			41,910	40,431	38,952
	1⅜"		44,323	42,844	41,365
1½ "			47,803	46,324	44,845
	1¾ "		53,746	52,267	50,788
2"			59,614	58,135	56,656
	2¼ "		65,710	64,231	62,762
2½ "			75,184	73,705	72,226
	2¾ "		81,534	80,055	78,576
3"			87,884	86,405	84,926
	3¼ "		93,980	92,501	91,022
3½ "			100,330	98,851	97,372
	3¾ "		106,680	105,201	103,722
4"			113,030	111,551	110,072
	4½ "		125,730	124,251	122,772
5"			138,430	136,951	135,472
	5½ "		151,130	148,651	148,172
6"			163,830	162,351	160,872

Parameters such as the quality of the pipe thread, its compliance with the pipe axis play a key role in the installation of plumbing and heating systems... In some cases, do-it-yourself cutting with a die is used. I must say that this work difficult, ineffective and time-consuming. It is better to cut with a cutter using a lathe.

General thread information

Pipe threads are protrusions and depressions with the same cross-section, evenly spaced on a cylindrical or conical surface (for example, nuts, screws, bolts). They are located along a helical line with the same pitch.

In everyday life, parts with a cylindrical thread are usually used. However, there are other types of it. There are two defining parameters for metric threads: pitch and diameter. Inch threads are so named because their defining characteristics are the diameter, expressed in inches or fractions of an inch. Also important parameter in this case, the number of turns per inch is counted. The size in inches denotes the clearance in the element, the outer diameter of the part is large.

Pipe thread table according to GOST

Important: One inch equals 2.54 cm. There is also another unit of measurement - pipe inch. It is equal to 33, 249 mm. What is this inch unit? They brought it out like this: to the value in inches, a value was added that characterizes the thickness of both walls of the pipe.

There are two types of pipes, the classification of which is pipe inch:

Product with an outer diameter of 33, 249 mm;
Product with an outer diameter of 21.25 mm.

Inch thread is a set of parameters required to connect pipes, fittings and other parts. It differs from metric, among other things, in such features as:

Pointed crests-depressions;
Rounded tops of hills.

Dimensions (edit)

In domestic conditions, most often you can find pipes with the following parameters and dimensions determined by GOST:

Thread 14 threads per 1 inch. In this case, the step is equal to 1.814 mm. The diameter can be ½ or ¾;
11 threads per 1 inch. In this case, the step is equal to 2.309 mm. The diameter can be 1, 1 ¼, 1 1/2, 2.

Inch threads are only available on pipelines no larger than 6 ". If the parameters of the pipe are larger, it is mounted into the system by means of welding. Its designations according to GOST: G (the value of the passage of the elements, indicated in inches), A, B (the degree of accuracy of the diameters).

Many parameters are required to select inch pipes. For this purpose, there are a number of tables in which all the important values are indicated. There are tables from which you can find out the steps and their ratio with threads per inch. This way you can quickly and easily get acquainted with all the necessary information. You can find all the tables you need on our website. They will help not only amateurs, but also professionals in working with pipes.

It would seem that in the pipes is complex? Connect and twist ... But, if you are not a plumber and not an engineer with a specialized education, then questions will certainly arise for the answers to which you will have to go wherever you look. And most likely the first thing they look at is the Internet)

Earlier we talked about diameters metal pipes in this material. Today we will try to clarify the threaded connections of pipes for various purposes. We tried not to clutter up the article with definitions. Basic terminology contains GOST 11708-82 which everyone can familiarize themselves with.

Cylindrical pipe thread. GOST 6357 - 81

Direction: Left

Accuracy class: Class A (increased), Class B (normal)

Why inches?

The inch size came to us from our Western colleagues, since the requirements of the acting in the post-Soviet space GOST a formulated on the basis of the thread BSW(British Standard Whitworth or Whitworth thread). Joseph Whitworth (1803 - 1887), a design engineer and inventor back in 1841, demonstrated the screw profile of the same name for detachable joints and positioned it as a universal, reliable and convenient standard.

This type of thread is used both in the pipes themselves and in the elements. pipe connections: locknuts, couplings, elbows, tees ( see picture above). In the cross-section of the profile, we see an isosceles triangle with an angle of 55 degrees and rounding at the tops and valleys of the contour, which are made for a high tightness of the connection.

Threads can be tapped up to 6 ”. All larger pipes are fixed by welding for a secure connection and to prevent rupture.

Symbol in the international standard

International: G

Japan: PF

UK: BSPP

Specify the letter G and the bore diameter (inner Ø) of the pipe in inches. The outer diameter of the thread itself is not present in the designation.

Example:

G 1/2- external cylindrical pipe thread, internal pipe Ø 1/2 "". The outer diameter of the pipe will be 20.995 mm, the number of steps on a length of 25.4 mm will be 14.

The accuracy class (A, B) and the direction of the turns (LH) can also be indicated.

For example:

G 1 ½ - B- cylindrical pipe thread, internal Ø 1 ½ inch, accuracy class B.

G1 ½ LH- B- Cylindrical pipe thread, internal Ø 1 ½ ", accuracy class B, left-hand.

The make-up length is indicated by the last in mm: G 1 ½ -B-40.

For cylindrical internal pipe threads, only the pipe Ø for which the hole is intended will be indicated.

Straight pipe thread size table

Thread size	Thread pitch, mm	Threads per inch	Thread diameters
	Thread pitch, mm	Threads per inch

How to determine the pitch of an inch thread

Here is a picture for you from the English-speaking Internet, which clearly demonstrates the technique. A pipe thread is characterized not by the size between the tops of the profile, but by the number of turns per inch along the axis of the thread. An ordinary tape measure or ruler can help. We apply, measure out one inch (25.4 mm) and visually count the number of steps.

In the picture with an example ( see above) threads - literally "threads" in English. In this case, there are 18 of them. one inch.

It's even easier if you have an inch gauge lying around in your toolbox. It is very convenient to carry out measurements, but it must be remembered that dummy threads can differ in the angle of the top of 55 ° and 60 °.

Tapered pipe threads

drawing pipe tapered threads

Tapered pipe thread GOST 6211-81 (1st standard size)

Parameter unit: Inch

Corresponds to a rounded section of a cylindrical pipe thread with an angle of 55 °. Cm. upper part (I) of the 3D image "drawing of pipe tapered threads".

Symbol

International: R

Japan: PT

UK: BSPT

The letter R and the nominal diameter Dy are indicated. The R designation means exterior view threads, Rc internal, Rp internal cylindrical. By analogy with straight pipe threads, LH is used for left-hand threads.

Examples:

R1 ½- external pipe tapered thread, nominal diameter Dy = 1 ½ inch.

R1 ½ LH- external pipe tapered thread, nominal diameter Dy = 1 ½ inch, left-hand.

Tapered inch thread GOST 6111 - 52 (2nd standard size)

Parameter unit: Inch

Has a profile angle of 60 °. Cm. bottom part (II) of the three-dimensional image "drawing of pipe tapered threads". It is used in pipelines (fuel, water, air) machines and machine tools with a relatively low pressure. The use of this type of connection assumes tightness and thread locking without additional special means(linen threads, yarn with red lead).

Symbol

Example: K ½ GOST 6111 - 52

It stands for: tapered inch thread with an outer and inner diameter in the main plane approximately equal to the outer and inner Ø of a cylindrical pipe thread G ½

Table of the main parameters of tapered inch threads

Thread size designation (d, inches)	Number of threads per 1 "n	Thread pitch S, mm	Thread length, mm		Outside diameter of the thread in the main plane d, mm
Thread size designation (d, inches)	Number of threads per 1 "n	Thread pitch S, mm	Working l1	From the end of the pipe to the main plane l2	Outside diameter of the thread in the main plane d, mm
1/16	27	0,941	6,5	4,064	7,895
1/8	27	0,941	7,0	4,572	10,272
1/4	18	1,411	9,5	5,080	13,572
3/8	18	1,411	10,5	6,096	17,055
1/2	14	1,814	13,5	8,128	21 793
3/4	14	1,814	14,0	8,611	26,568
1	11 1/2	2,209	17,5	10,160	33,228
1 1/4	11 1/2	2,209	18,0	10,668	41,985
1 1/2	11 1/2	2,209	18,5	10,668	48,054
2	11 1/2	2,209	19,0	11,074	60,092

Metric tapered thread. GOST 25229 - 82

Parameter unit: mm

Manufactured on surfaces with a taper of 1:16

Used when connecting pipelines. The angle at the top of the turn is 60 °. The main plane is offset relative to the end face ( see pic above).

Symbol

The letters MK are followed by an indication of the diameter in the main plane and the thread pitch in mm: MK 30x2

Metric Tapered Thread Size Chart

Thread diameter d for a row		Step P	Thread diameter in the main plane
1	2		d = D	d2 = D2	d1 = D1	l	l1	l2
6	---	1	6,000	5,350	4,917	8	2,5	3
8	---		8,000	7,350	6,917
10	---		10,000	9,350	8,917
12	---	1,5	12,000	11,026	10,376	11	3,5	4
---	14		14,000	13,026	12,376
16	---		16,000	15,026	14,376
---	18		18,000	17,026	16,376
20	---		20,000	19,026	18,376
---	22		22,000	21,026	20,376
24	---		24,000	23,026	22,376
---	27	2	27,000	25,701	24,835	16	5	6
30	---		30,000	28,701	27,835
---	33		33,000	31,701	30,835
36	---		36,000	34,701	33,835

Characteristic of parallel pipe / inch threads relative to metric

Main characteristics of "inch" and "pipe" cylindrical threads in relation to "metric" threads for basic dimensions.

Nominal thread diameter in dm	Inch thread		Pipe thread
Nominal thread diameter in dm	outer diameter, in mm	number of threads per 1 "	outer diameter, in mm	number of threads per 1 "

BASIC PARAMETERS OF INCH THREADS
(BSW (Ww), BSF, UNC, UNF standards)

The tops and valleys of an inch thread, similar to a metric one, are flat. The pitch of an inch thread is determined by the number of threads (turns) per inch 1 ", but its top angle is 55 ° (Whitworth's thread is British BSW (Ww) and BSF), the nose angle is 60 ° (American UNC and UNF ).

Outer thread diameter is measured in inches 1 "= 25.4 mm- shpich (") symbol inch. Inch thread is characterized by the number of threads per inch. According to American standards, inch threads are made with coarse (UNC) and fine (UNF) pitches.
NPSM- American standard for inch cylindrical pipe thread.
NPT- American standard for inch tapered threads.

Standards:

ASME / ANSI B1.1- 2003 Unified Inch Screw Threads, UN & UNR Thread Form
ASME / ANSI B1.10M- 2004 Unified Miniature Screw Threads
ASME / ANSI B1.15- 1995 Unified Inch Screw Threads, UNJ Thread Form

AMERICAN INCH THREAD

The main parameters of an inch thread:

d (D)- the outer diameter of the thread, respectively, of the bolt and nut;
d p (D p)- the average diameter of the thread, respectively, of the bolt and nut;
d i (D i)- internal diameter of the thread, respectively, of the bolt and nut;
n- the number of threads per inch.

American Coarse Thread - UNS

Thread sizes, inches (mm)	D	*D p*	*D i*	Thread sizes, inches (mm)	D	*D p*	*D i*
Thread sizes, inches (mm)				Thread sizes, inches (mm)
№1 (1,8542)
№2 (2,1844)				1 (25,4)
№3 (2,5146)				1 1/8 (28,58)
№4 (2,8448)				1 1/4 (31,75)
№5 (3,1750)				1 3/8 (34,925)
№6 (3,5052)				1 1/2 (38,10)
№8 (4,1656)				1 3/4 (44,45)
№10 (4,8260)
№12 (5,4864)				2 (50,8)
				2 1/4 (57,15)
1/4 (6,3500)				2 1/2 (63,5)
5/16 (7,9375)				2 3/4 (69,85)
3/8 (9,5250)
7/16 (11,1125)				3 (76,2)
1/2 (12,700)				3 1/4 (82,55)
9/16 (14,2875)				3 1/2 (88,9)
5/8 (15,8750)				3 3/4 (95,25)
3/4 (19,0500)				4 (101,6)
7/8 (22,2250)

American Fine Pitch Thread - UNF

Thread sizes, inches (mm)	D	*D p*	*D i*	Thread sizes, inches (mm)	D	*D p*	*D i*
Thread sizes, inches (mm)				Thread sizes, inches (mm)
№0 (1,524)				3/8 (9,525)
№1 (1,8542)				7/16 (11,1125)
№2 (2,1844)				1/2 (12,700)
№3 (2,5146)				9/16 (14,2875)
№4 (2,8448)				5/8 (15,875)
№5 (3,1750)				3/4 (19,050)
№6 (3,5052)				7/8 (22,225)
№8 (4,1656)
№10 (4,8260)				1 (25,4)
№12 (5,4864)				1 1/8 (28,58)
				1 1/4 (31,75)
1/4 (6,350)				1 3/8 (34,925)
5/16 (7,9375)				1 1/2 (38,10)

American thread with extra fine pitch - UNEF

Thread sizes, inches (mm)	D	*D p*	*D i*	Thread sizes, inches (mm)	D	*D p*	*D i*
Thread sizes, inches (mm)				Thread sizes, inches (mm)
№12 (5,4864)
				1 (25,4)
1/4 (6,350)				1 1/16 (26,987)
5/16 (7,9375)				1 1/8 (28,58)
3/8 (9,525)				1 3/16 (30,162)
7/16 (11,1125)				1 1/4 (31,75)
1/2 (12,700)				1 5/16 (33,337)
9/16 (14,2875)				1 3/8 (34,925)
5/8 (15,875)				1 7/16 (36,512)
11/16 (17,462)				1 1/2 (38,10)
3/4 (19,050)				1 9/16 (39,687)
13/16 (20,637)				1 5/8 (41,27)
7/8 (22,225)				1 11/16 (42,86)
15/16 (23,812)

Thread sizes are the outside diameter of a thread, expressed in fractions of an inch. One of the main characteristics of an inch screw thread is the number of turns per inch of thread length (n). The number of turns and the thread pitch P are related by the ratio:

American standards provide for two forms of thread:

Flat-root thread, which is designated by the letters UN;
- thread with a radial root, which is designated by the letters UNR.

The standard defines three classes of thread accuracy. These classes are designated as 1A, 2A, 3A, 1B, 2B, 3B. Accuracy classes 1A, 2A, 3A refer to external threads; accuracy classes 1B, 2B, 3B refer to internal threads. Accuracy class 1A, 1B is the coarsest and is used in cases where quick and easy assembly is required, even with partially dirty and dented threads. Accuracy class 2A, 2B is the most common and is used for general-purpose threads. Accuracy class 3A, 3B makes the most stringent requirements for threads and is used in cases where it is required to ensure a minimum clearance in the threaded connection.

Thread designation... The nominal size is recorded first, followed by the number of threads per inch of thread, the thread group symbols, and the precision class symbol. The letters LH at the end of the entry indicate left-hand thread... The nominal size is the outside diameter, defined as a fractional size or thread number, or their decimal equivalent.
For example: 1/4 - 20UNS - 2A or 0.250 - 20UNC - 2A

BRITISH STANDARD INCH THREADS
(BSW (Ww) and BSF)

Identifier carvings	BSP the size in	thread pitch		largest diameter		smallest diameter		A / F mm	length mm	pipes				thread hole diameter (for drill) mm
Identifier carvings	BSP the size in	in (TPI)	mm	mm	in	mm	in	A / F mm	length mm	DN mm	OD mm	OD in	thickness mm	BSP.PL (Rp)	BSP.F (G)
-1	1 / 16	28	0,907	7,723	0,304	6,561	0,2583		4 ± 0.9					6,60	6,80
-2	1 / 8	28	0,907	9,728	0,383	8,565	0,3372	15	4 ± 0.9	6	10,2	0,40	2	8,60	8,80
-4	1 / 4	19	1,337	13,157	0,518	11,445	0,4506	19	6 ± 1.3	8	13,5	0,53	2,3	11,50	11,80
-6	3 / 8	19	1,337	16,662	0,656	14,950	0,5886	22/23	6.4 ± 1.3	10	17,2	0,68	2,3	15,00	15,25
-8	1 / 2	14	1,814	20,955	0,825	18,633	0,7336	27	8.2 ± 1.8	15	21,3	0,84	2,6	18,75	19,00
-10	5 / 8	14	1,814	22,911	0,902	20,589	0,8106			16			2,6	-	21,00
-12	3 / 4	14	1,814	26,441	1,041	24,120	0,9496	32	9.5 ± 1.8	20	26,9	1,06	2,6	24,25	24,50
-16	1	11	2,309	33,249	1,309	30,292	1,1926	43	10.4 ± 2.3	25	33,7	1,33	3,2	30,40	30,75
-20	1 1 / 4	11	2,309	41,910	1,650	38,953	1,5336	53	12.7 ± 2.3	32	42,4	1,67	3,2	39,00	39,50
-24	1 1 / 2	11	2,309	47,803	1,882	44,846	1,7656	57	12.7 ± 2.3	40	48,3	1,90	3,2	45,00	45,00
-32	2	11	2,309	59,614	2,347	56,657	2,2306	70	15.9 ± 2.3	50	60,3	2,37	3,6	56,75	57,00
-40	2 1 / 2	11	2,309	75,184	2,960	72,227	2,8436		17.5 ± 3.5	65	76,1	3,00	3,6
-48	3	11	2,309	87,884	3,460	84,927	3,3436		20.6 ± 3.5	80	88,9	3,50	4
-64	4	11	2,309	113,030	4,450	110,073	4,3336		25.5 ± 3.5	100	114,3	4,50	4,5
-80	5	11	2,309	138,430	5,450	135,472	5,3335		28.6 ± 3.5	125	139,7	5,50	5
-96	6	11	2,309	163,830	6,450	160,872	6,3335		28.6 ± 3.5	150	165,1	6,50	5