Internal thread 1 2 inches. Pipe thread sizes

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 specialized education, then questions will definitely arise 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 an 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 larger pipes are fixed by welding to ensure a reliable connection and prevent rupture.

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. Outside diameter The thread itself is not present 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

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
			Working l1	From the end of the pipe to the main plane l2
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
	outer diameter, mm		number of threads per 1"	outer diameter, mm		number of threads per 1"

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	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 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.

Main settings 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.

inches	mm.	inches	mm.	inches	mm.	inches	mm.	inches	mm.
-	-	1	25,4	2	50,8	3	76,2	4	101,6
1/8	3,2	1 1/8	28,6	2 1/8	54,0	3 1/8	79,4	4 1/8	104,8
1/4	6,4	1 1/4	31,8	2 1/4	57,2	3 1/4	82,6	4 1/4	108,8
3/8	9,5	1 3/8	34,9	2 3/8	60,3	3 3/8	85,7	4 3/8	111,1
1/2	12,7	1 1/2	38,1	2 1/2	63,5	3 1/2	88,9	4 1/2	114,3
5/8	15,9	1 5/8	41,3	2 5/8	66,7	3 5/8	92,1	4 5/8	117,5
3/4	19,0	1 3/4	44,4	2 3/4	69,8	3 3/4	95,2	4 3/4	120,6
7/8	22,2	1 7/8	47,6	2 7/8	73,0	3 7/8	98,4	4 7/8	123,8

Inch thread parameters

Outer diameter of the connected pipe		SAE Thread Rating	UNF thread rating	Outer thread diameter, mm	Average thread diameter, mm	Thread pitch
mm	inch					mm	threads/inch
6	1/4""""	1/4""""	7/16""""-20	11,079	9,738	1,27	20
8	5/16""""	5/16""""	5/8""""-18	15,839	14,348	1,411	18
10	3/8""""	3/8""""	5/8""""-18	15,839	14,348	1,411	18
12	1/2""""	1/2""""	3/4""""-16	19,012	17,33	1,588	16
16	5/8""""	5/8""""	7/8""""-14	22,184	20,262	1,814	14
18	3/4""""	3/4""""	1""""-14	25,357	23,437	1,814	14
18	3/4""""	---	1""""1/16-14	26,947	25,024	1,814	14
20	7/8""""	---	1""""1/8-12	28,529	26,284	2,117	12
22	7/8""""	7/8""""	1""""1/4-12	31,704	29,459	2,117	12
22	7/8""""	---	1""""3/8-12	34,877	32,634	2,117	12
25	1""""	1""""	1""""1/2-12	38,052	35,809	2,117	12

Copper conductors, wires and cables

Conductor cross-section, mm	Copper conductors, wires and cables
	Voltage, 220 V		Voltage, 380 V
	current, A	power, kWt	current, A	power, kWt
1,5	19	4,1	16	10,5
2,5	27	5,9	25	16,5
4	38	8,3	30	19,8
6	46	10,1	40	26,4
10	70	15,4	50	33,0
16	85	18,7	75	49,5
25	115	25,3	90	59,4
35	135	29,7	115	75,9
50	175	38,5	145	95,7
70	215	47,3	180	118,8
95	260	57,2	220	145,2
120	300	66,0	260	171,6

Aluminum conductors, wires and cables

Cross-section of current-carrying conductor, mm	Aluminum conductors, wires and cables
	Voltage, 220 V		Voltage, 380 V
	current, A	power, kWt	current, A	power, kWt
1,5	19	4,1	16	10,5
2,5	27	5,9	25	16,5
4	38	8,3	30	19,8
6	46	10,1	40	26,4
10	70	15,4	50	33,0
16	85	18,7	75	49,5
25	115	25,3	90	59,4
35	135	29,7	115	75,9
50	175	38,5	145	95,7
70	215	47,3	180	118,8
95	260	57,2	220	145,2
120	300	66,0	260	171,6

Inch thread sizes

	Thread diameter in mm			Thread pitch in mm	Number of threads per 1"
	outer d	average d	internal d
3/16	4,762	4,085	3,408	1,058	24
1/4	6,350	5,537	4,724	1,270	20
5/16	7,938	7,034	6,131	1,411	18
3/8	9,525	8,509	7,492	1,588	16
1/2	12,700	11,345	9,989	2,117	12
5,8	15,875	14,397	12,918	2,309	11
3/4	19,05	17,424	15,798	2,540	10
7/8	22,225	20,418	18,611	2,822	9
1	25,400	23,367	21,334	3,175	8
1 1/8	28,575	26,252	23,929	3,629	7
1 1/4	31,750	29,427	27,104	3,629	7
1 1/2	38,100	35,39	32,679	4,233	6
1 3/4	44,450	41,198	37,945	5,080	5
2	50,800	47,186	43,572	5,644	4 1/2

Nominal thread diameter in inches
	Thread diameter in mm			Thread pitch in mm	Number of threads per 1"
	outer d	average d	internal d
1/8	9,729	9,148	8,567	0,907	28
1/4	13,158	12,302	11,446	1,337	19
3/8	16,663	15,807	14,951	1,337	19
1/2	20,956	19,794	18,632	1,814	14
5/8	22,912	21,750	20,588	1,814	14
3/4	26,442	25,281	24,119	1,814	14
7/8	30,202	29,040	27,878	1,814	14
1	33,250	31,771	30.293	2,309	11
1 1/8	37,898	36,420	34,941	2,309	11
1 1/4	41,912	40,433	38,954	2,309	11
1 3/8	44,325	32,846	41,367	2,309	11
1 1/2	47,805	46,326	44,847	2,309	11
1 3/4	53,748	52,270	50,791	2,309	11
2	59,616	58,137	56,659	2,309	11

Unit conversion table

Conversion of energy units	Conversion of pressure units
1 J = 0.24 cal	1 Pa = 1 N/m*m
1 kJ = 0.28 Wh	1 Pa = 0.102 kgf/m*m
1 W = 1 J/s	1 atm =0.101 mPa =1.013 bar
1 cal = 4.2 J	1 bar = 100 kPa = 0.987 atm
1 kcal/h = 1.163 W	1 PSI = 0.06895 bar = 0.06805 atm

Size conversion tables: simple and fast

The process of selecting the required cross-sectional sizes of threads, cables and pipes often takes a lot of time. In addition to the fact that it is necessary to select the appropriate dimensions, taking into account the parameters of the equipment, the customer has to independently convert the data into suitable units of measurement. This process requires significant time.

We simplify this task because we invite you to use ready-made translation tables. On the page of our website you will find tables that will help you easily select the necessary threads for inch pipes, copper and aluminum wires and cables. Also, you can use the translation table inch sizes in metric, thereby accurately calculating the required cross-sectional dimensions.

Unfortunately, most equipment manufacturers leave the customer alone with the calculations. Therefore, a person has to independently search the Internet for translation tables in order to select optimal sizes wire sections and pipe diameters.

We value the time of our clients, providing everyone with the opportunity to use ready-made solutions. Translated in our tables standard sizes from inches to millimeters.

On this page you will also find translations of basic energy units and pressure units, therefore, you will be able to choose the right refrigeration equipment, taking into account the individual placement conditions and operating modes of the units.

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 spread of detachable threaded connections was hampered by the lack of standardization, which made it impossible to ensure the interchangeability of products. The talented English engineer Charles Whitworth solved this problem. He developed a unified system of sizes and designations, using the English inch for this. This is how inch thread was born. And all sizes are listed in the table according to GOST.

Options

Inch thread is plug connection triangular profile, the angle of the vertices 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 pipe connection and in the manufacture of hydraulic sealing elements.

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

• The outer diameter is the distance between the tops of the threads located on opposite sides of the 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 is difficult to measure under normal conditions, and there is a reference table for threads 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 greater the fluid pressure it 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.

Inch thread designation in technical documentation Let's look at 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 are distinguished by higher mechanical characteristics due to a smoother distribution of voltage waves between turns. The knurling also has high performance, which allowed it to find extensive use 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 specified types under hand tools depending on the type of thread. Carry out cutting. This process is repeated to improve purity and accuracy.

On a 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 is more effective compared to manual cutting, but requires certain qualifications from the turner.

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.

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 the top points of the 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 section of the product on which the pipe thread is made, its pitch 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 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 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 different units measurements. 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.
• If the bolt has formed a tight threaded connection with the coupling or fitting, 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 size of the outer diameter 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 by hand or mechanical method.

Manual thread cutting

Cutting a thread using a hand tool, 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.

Return