Pipe thread. Pipe thread sizes

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

The peaks and valleys of the inch thread profile, similar to the metric thread, are cut flat. The pitch of an inch thread is determined by the number of threads (turns) per inch 1", but its apex angle is 55° (Whitworth thread - British standard BSW (Ww) and BSF), apex angle is 60° (American standard UNC and UNF ).

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

Basic parameters of inch thread:

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

American thread with coarse pitch - 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 outer diameter of the thread, expressed in fractional 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 thread pitch P are related by the relation:

American standards provide two thread forms:

A thread with a flat recess, which is designated by the letters UN;
- thread with a radius cavity, 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 fast and easy assembly, even with partially dirty and dented threads. Accuracy class 2A, 2B are the most common and are used for threads general purpose. Accuracy class 3A, 3B imposes the most stringent requirements on threads and is used in cases where it is necessary to ensure a minimum clearance in a threaded connection.

Thread designation. First recorded nominal size, then the number of threads per inch of thread, thread group symbols, and accuracy class symbol. The letters LH at the end of the entry indicate left-hand thread. 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)

Designation threads	BSP size in	thread pitch		largest diameter		smallest diameter		A/F mm	length mm	pipes				thread hole diameter (for drill) mm
Designation threads	BSP size in	in (TPI)	mm	mm	in	mm	in	A/F mm	length mm	DN mm	O.D. mm	O.D. 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

General information about threads

Pipe threads are protrusions and recesses 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 cylindrical threads are usually used. However, there are other types of it. There are two defining parameters of a metric thread: pitch and diameter. Inch thread is so called because its defining characteristics are the diameter, expressed in inches or fractions of an inch. Also an important parameter in this case is the number of turns located per inch length. The size in inches indicates the clearance in the element, while the outer diameter of the part is larger.

Pipe thread table according to GOST

Important: One inch equals 2.54 cm. There is also another unit of measurement - a pipe inch. It is equal to 33.249 mm. What is this inch unit of measurement? It was derived like this: to the value in inches we added a value characterizing the thickness of both walls of the pipe.

There are two types of pipes, the parameter for classification of which is the 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 necessary for connecting pipes, fittings and other parts. Among other things, it differs from metric in such features as:

Pointed ridges and depressions;
Rounded hilltops.

Dimensions

IN living 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 pitch is 1.814 mm. The diameter can be ½ or ¾;
11 threads per 1 inch. In this case, the pitch is 2.309 mm. The diameter can be 1, 1 ¼, 1 1/2, 2.

Inch threads are only used on pipelines whose dimensions do not exceed 6″. If the pipe parameters are larger, it is installed into the system using welding work. Its designations according to GOST: G (the value of the passage of elements, indicated in inches), A, B (degree of diameter accuracy).

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

Fastening with threads has been known since antiquity. Scientists are still finding remains of parts that look like modern screws and nuts. But carving became most widespread during the industrial revolution of the 18th century. Initially, the distribution of plug-in threaded connection was hampered by the lack of standardization, which made it impossible to ensure interchangeability of products. The talented English engineer Charles Whitworth solved this problem. He developed unified system sizes and designations using the English inch. This is how inch thread was born. And all sizes are listed in the table according to GOST.

Options

An inch thread is a detachable connection of a triangular profile, the angle of the vertices of which is 55 degrees. Its unit of measurement is inches. It is worth noting right away that in Russia the use of inch threads when designing new products is prohibited. Its use is permitted only in the case of the manufacture of spare parts of equipment for which inch threads have already been manufactured. In addition, it is allowed to use this thread as a pipe connection and in the manufacture of sealing hydraulic elements.

Inch, like any other, is characterized by the following basic parameters:

Outer diameter - the distance between the tops of the turns located on opposite sides thread. The larger the value of this parameter, the greater the axial load the thread can withstand. Downside medal is the deterioration of tightness associated with the accumulation of errors during thread cutting.
Nominal (average) diameter is a circle inscribed in the thread profile, the diameter of which depends on the pitch, and occupies an intermediate position between the internal and external diameters. This parameter in normal conditions is difficult to measure and there is a thread reference table to determine it.
Internal diameter is the diameter of a circle inscribed along the recesses of the thread profile.
Pitch - the distance between adjacent scallops of a threaded connection. This parameter is measured in the number of threads per inch. The pitch size characterizes the value and distribution of stress between the turns of inch threads. Designers in their practice increase the pitch when subjecting the thread to large mechanical loads. If requirements are imposed on the thread to maintain tightness, then the pitch is reduced.
The angle of rise of the turns is the angle between the sides of the profile of the turns. Initially, its value for all types of inch threads was 55 degrees. But now, inch threads with a profile angle of 60 degrees are becoming more and more common.

Types of inch threads

There are many types of threaded connections, the dimensions of which are inches, but among them in Russia the following main types are distinguished:

Pipe cylindrical
Pipe conical

Each category has its own characteristics. Cylindrical pipe threads are regulated by GOST 6357-81. Thread sizes are standardized and listed in a special table. These inch threads, first of all, are distinguished by a finer pitch, which means fewer turns per inch.

Table. Pipe cylindrical thread. GOST 6357-81.

Thread designation		Number of steps z at a length of 25.4 mm	Step P	Thread diameter			Working height of profile H 1	Curvature radius R	H	H/6
1st row	2nd row			outer d = D	average d 2 = D 2	internal d 1 = D 1
1/16" 1/8"	-	28	0,907	7,723	7,142	6,561	0,580777	0,124557	0,871165	0,145194
				9,728	9,147	8,566
1/4" 3/8"	-	19	1,337	13,157	12,301	11,445	0,856117	0,183603	1,284176	0,214029
				16,662	15,806	14,950
1/2"	5/8"	14	1,814	20,955	19,793	18,631	1,161553	0,249115	1,742331	0,290389
				22,911	21,749	20,587
				26,441	25,279	24,117
				30,201	29,039	27,877
1"	1 1/8" 1 3/4"	11	2,309	33,249	31,770	30,291	1,478515	0,317093	2,217774	0,369629
				37,897	36,418	34,939
				41,910	40,431	38,952
				44,323	42,844	41,365
				47,803	46,324	44,845
				53,746	52,267	50,788
				59,614	58,135	56,656
2 1/2" 3 1/2"	2 1/4" 3 3/4"			65,710	64,231	62,752
				75,184	73,705	72,226
				81,534	80,055	78,576
				87,884	86,405	84,926
				93,980	92,501	91,022
				100,330	98,851	97.372
				106,680	105,201	103,722
4"	4 1/2" 5 1/2"			113,030	111,551	110.072
				125,730	124,251	122,772
				138,430	136,951	135,472
				151,130	149,651	148,172
				163,830	162,351	160,872
When choosing thread sizes, row 1 should be preferred to row 2.

Its second difference is its more rounded profile. It promotes closer contact of the turns to each other, which reduces the likelihood of leakage when transporting liquid through this threaded connection.

Cylindrical pipe threads are cut on pipes whose diameter does not exceed 6 inches. For pipes larger than this size, the use of high-precision equipment is required, which increases production costs. In this case, it is more efficient, both technologically and financially, to fasten the pipes by welding.

Tapered pipe threads are represented by GOST 6211-81. The size table, deviation limits and load values are described in this standard. In terms of the type of thread profile, a conical thread is similar to an inch thread, but has 2 quite important differences.

Tapered pipe thread. GOST 6211-81.

Thread size designation	Step P	Number of steps per length 25.4 mm	H	H 1	C	R	Thread diameters in the main plane			Thread length
							d = D	d2 = D2	d 1 = D 1	l 1	l 2
1/16"	0,907	28	0,870935	0,580777	0,145079	0,124511	7,723	7,142	6,561	6,5	4,0
1/8"							9,728	9,147	8,566
1/4"	1,337	19	1,283837	0,856117	0,213860	0,183541	13,157	12,301	11,445	9,7	6,0
3/8"							16,662	15,806	14,950	10,1	6,4
1/2"	1,814	14	1,741870	1,161553	0,290158	0,249022	20,955	19,793	18,631	13,2	8,2
3/4"							26,441	25,279	24,117	14,5	9,5
1"	2,309	11	2,217187	1,478515	0,369336	0,316975	33,249	31,770	30,291	16,8	10,4
1 1/4"							41,910	40,431	38,952	19,1	12,7
1 1/2"							47,803	46,324	44,845
2"							59,614	58,135	56,656	23,4	15,9
2 1/2"							75,184	73,705	72,226	26,7	17,5
3"							87,884	86,405	84,926	29,8	20,6
3 1/2"							100,330	98,851	97,372	31,4	22,2
4"							113,030	111,551	110,072	35,8	25,4
5"							138,430	136,951	135,472	40,1	28,6
6"							163,830	162,351	160,872

First of all, there are two types of profile angles: 55 and 60 degrees. The second difference is that the thread is cut along a cone, due to which conical threads have such a quality as self-sealing (a table with taper values is indicated in the reference literature). Therefore, fastening joints using them do not require the use of additional sealing elements: flax thread, yarn with red lead, etc.

Markings and accuracy classes

There are 3 classes of thread accuracy: first (the coarsest), second and third (the most precise). The choice of one class or another depends on 2 factors: the dimensions of the thread diameter taken from the table, the fluid pressure in the pipeline. The higher the thread class, the more pressure liquid she can withstand.

Dimensions are checked for compliance with a certain accuracy class using special gauges. This method allows you to most reliably determine whether the thread matches the required dimensions, but it is more labor-intensive. This method is effective in conditions of multi-batch production of parts that require high precision. When the production volume is not so large and there are no increased requirements for accuracy, the thread sizes are controlled as follows:

The dimensions of the outer diameter are measured using calipers, micrometers and other mechanical measuring instruments. The readings are then checked against a reference table.
The pitch dimensions are determined by applying special dies, for example an inch thread gauge. Then the resulting number of turns per inch is correlated with the value of the inch thread size table. The easiest way to measure the thread pitch is to take a ruler, mark 25.4 millimeters on it and count how many turns are included in this segment. Let us immediately note that this is the roughest method and is not suitable for measuring threads with the third and second class of accuracy.

Let's look at the designation of inch threads in technical documentation using an example:

The letter "G" means that the pipe thread is cylindrical. According to Russian standards, a conical pipe is designated by the letter “K”.

The number "2" indicates the size of the outer diameter. The unit of measurement is inches. Thread sizes and their options are fully regulated by GOSTs and are listed in special tables.

The letters "LH" indicate that the thread has a left-hand screw direction. The absence of this designation indicates the right direction.

The number “2” characterizes the accuracy class. The table of deviation limits is indicated in GOST. The number “40” is the size characterizing the length of screwing.

Making threads

To obtain inch cuts, 2 main methods are used:

Knurling;
Slicing.

Rolled ones are made using special thread rolling rollers, the profile of which follows the contour of the thread. The workpiece is placed between the rollers, and the threads are rolled to the required dimensions.

Threads made using this method have higher mechanical characteristics due to a smoother distribution of stress waves between the turns. Also, knurling has high productivity, which has allowed it to be widely used in mass production.

The disadvantage of the rolling method is the difficulty of making rollers. Their accuracy should be high level. Otherwise, it is very difficult to guarantee the required thread sizes. The second point is the material of the rollers. It must have improved mechanical properties. Typically, high-alloy stamped steels are used for this. All this makes the knurling method very expensive from a financial point of view.

Cut threads are easier to manufacture, but mechanical properties, especially in terms of endurance, are noticeably inferior to the knurled ones. This is due to the presence of sharper profile edges and, accordingly, more high value voltage coefficient.

The product is cut in two ways:

Manually.
Using a lathe.

At manual cutting use a tap (for the inner line) and a die (for the outer one). The pipe is clamped. One of the indicated types of available tools is put on and screwed onto its end, depending on the type of thread. Carry out cutting. For improved purity and accuracy this process repeat.

On lathe The algorithm of actions is quite similar. Only the pipes are clamped not in a vice, but in a machine chuck. Next, the cutter is brought in, the thread feed is turned on, and the machine begins the manufacturing process. This method more effective compared to manual cutting, but requires certain qualifications from the turner.

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

So, those who have already encountered pipe threads have been 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 inch threads actually indicate the through hole of the pipe, and not the outer diameter of the thread. At the same time, by adding to the size of the hole in the pipe wall, we get the overestimated outer diameter that we are accustomed to in the designation of metric threads. Conventionally 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 of the pipe, they also increase accordingly, since the pipe with large diameter must have thicker walls than a pipe with a smaller diameter for the same operating pressure.

Pipe threads are divided into the following:

Cylindrical pipe thread

This is an inch thread based on BSW (British Standard Whitworth) thread and corresponds to BSP (British standard pipe thread) thread, has four pitch values 28,19,14,11 threads per inch. Cuts on pipes up to size 6", pipes over 6" are welded.

The profile angle at the apex is 55°, the theoretical profile height is Н=0.960491Р.

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, the numerical value of the nominal diameter of the pipe in inches (inch), the accuracy class of the average diameter (A, B), and the 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. Once again, we would like to remind you that it should be borne in mind that the nominal thread size corresponds to the pipe clearance in inches. The outer diameter of the pipe is in some proportion with this size and more accordingly to the thickness of the pipe walls.

Designation of cylindrical pipe thread size (G), steps and nominal values of 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

It would seem that there is something complicated in the pipes? Connect and twist... But, if you are not a plumber or an engineer with a specialized education, then you will definitely have questions for 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 already 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 the article with definitions. Basic terminology contains GOST 11708-82 which everyone can familiarize themselves with.

Pipe cylindrical thread. GOST 6357 - 81

Direction: Left

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

Why in inches?

The inch size came to us from Western colleagues, since the requirements of the current in the post-Soviet space GOST and are formulated on the basis of thread B.S.W.(British Standard Whitworth or Whitworth carving). Joseph Whitworth (1803 - 1887), a design engineer and inventor, demonstrated the screw profile of the same name for detachable connections back in 1841 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 of pipe connections: locknuts, couplings, elbows, tees ( see picture above). In the profile section we see isosceles triangle with an angle of 55 degrees and roundings at the tops and bottoms of the contour, which are made for high tightness of the connection.

Threading of threaded connections is carried out on sizes up to 6”. All pipes larger size To ensure reliable connection and prevent rupture, they are fixed by welding.

Symbol in the international standard

International: G

Japan: PF

UK: BSPP

The letter G and the bore diameter (internal Ø) of the pipe are indicated in inches. The outer diameter of the thread itself is not included in the designation.

Example:

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

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

For example:

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

G1 ½ LH- B- cylindrical pipe thread, internal Ø 1 ½ inches, accuracy class B, left.

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

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

Parallel Pipe Thread Size Chart

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

I’ll give you a picture from the English-language Internet that clearly demonstrates the technique. Pipe threads are characterized not by the size between the tops of the profile, but by the number of turns per 1 inch along the thread axis. A regular tape measure or ruler can help. Apply it, measure one inch (25.4 mm) and visually count the number of steps.

In the picture with an example ( see above) threads - from English these are literally “threads of thread”. IN in this case there are 18 of them. by one inch.

It’s even easier if you have a thread gauge for inch threads lying around in your tool box. It is very convenient to take measurements, but it must be remembered that inch threads may differ in the apex angle of 55° and 60°.

Tapered pipe threads

drawing of pipe tapered threads

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

Parameter Unit: Inch

Corresponds to the rounded profile of a cylindrical pipe thread with an angle of 55°. Cm. top part (I) of the three-dimensional image "drawing of pipe tapered threads".

Symbol

International: R

Japan: PT

UK: BSPT

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

Examples:

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

R1 ½ LH- external pipe thread, nominal diameter Dy = 1 ½ inches, left.

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

Parameter Unit: Inch

Has a profile angle of 60°. Cm. lower part (II) of the three-dimensional image "drawing of pipe tapered threads". It is used in pipelines (fuel, water, air) of machines and machines with relatively low pressure. Usage of this type 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: inch conical 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 main parameters of tapered inch threads

Thread size designation (d, inches)	Number of threads per 1" n	Thread pitch S, mm	Thread length, mm		Outer thread diameter 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	Outer thread diameter 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

Produced 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 shifted relative to the end ( 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 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

Characteristics of cylindrical pipe/inch threads relative to metric

The main characteristics of "inch" and "pipe" cylindrical threads in relation to "metric" threads for basic sizes.

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