1 4" threaded hole. Pipe thread sizes. designation. guests Tools for internal threading

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 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.

Slicing threaded connection Available in sizes up to 6". All pipes bigger 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

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. The use of this type of connection assumes tightness and locking of the thread 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
	outside diameter, in mm		number of threads per 1"	outer diameter, mm		number of threads per 1"

Even though the slicing internal thread not classified as complex technological operations, there are some features of preparation for this procedure. Thus, it is necessary to accurately determine the dimensions of the preparation hole for threading, and also select the right tool, for which special tables of drill diameters for threads are used. For each type of thread, it is necessary to use the appropriate tool and calculate the diameter of the preparation hole.

Types and parameters of thread

The parameters by which threads are divided into Various types, are:

• units of diameter (metric, inch, etc.);
• number of thread starts (one-, two- or three-thread);
• the shape in which the profile elements are made (triangular, rectangular, round, trapezoidal);
• direction of rise of turns (right or left);
• location on the product (external or internal);
• surface shape (cylindrical or conical);
• purpose (fastening, fastening and sealing, chassis).

Depending on the above parameters, the following types of thread are distinguished:

• cylindrical, which is designated by the letters MJ;
• metric and conical, designated M and MK respectively;
• pipe, designated by the letters G and R;
• with a round profile, named after Edison and marked with the letter E;
• trapezoidal, designated Tr;
• round, used for installation of sanitary fittings, – Kr;
• thrust and thrust reinforced, marked as S and S45, respectively;
• inch thread, which can also be cylindrical and conical - BSW, UTS, NPT;
• used to connect pipes installed in oil wells.

Application of the tap

Before you start threading, you need to determine the diameter of the preparation hole and drill it. To facilitate this task, a corresponding GOST was developed, which contains tables that allow you to accurately determine the diameter of the threaded hole. This information makes it easy to select the drill size.

To cut metric threads on the inner walls of a hole made with a drill, a tap is used - a screw-shaped tool with cutting grooves, made in the form of a rod, which can have a cylindrical or conical shape. On its side surface there are special grooves located along its axis and dividing the working part into separate segments, which are called combs. The sharp edges of the combs are precisely the working surfaces of the tap.

In order for the turns of the internal thread to be clean and neat, and for its geometric parameters to correspond to the required values, it must be cut gradually, by gradually removing thin layers of metal from the surface being treated. That is why for this purpose they use either taps, the working part of which is divided along the length into sections with different geometric parameters, or sets of such tools. Single taps, the working part of which has the same geometric parameters along its entire length, are needed in cases where it is necessary to restore the parameters of an existing thread.

The minimum set with which you can sufficiently perform machining of threaded holes is a set consisting of two taps - rough and finishing. The first one cuts holes from the walls for cutting metric threads thin layer metal and forms a shallow groove on them, the second not only deepens the formed groove, but also cleans it.

Combination two-pass taps or sets consisting of two tools are used for tapping small diameter holes (up to 3 mm). To machine holes for larger metric threads, you must use a combination three-pass tool or a set of three taps.

Used for manipulating the tap special device- collar. The main parameter of such devices, which can have different design, is the size of the mounting hole, which must exactly match the size of the tool shank.

When using a set of three taps that differ both in their design and geometric parameters, the sequence of their use must be strictly observed. They can be distinguished from each other both by special marks applied to the shanks and by design features.

1. The tap with which the hole for cutting metric threads is processed first is different minimum diameter among all the tools of the set and cutting teeth, the upper part of which is greatly cut off.
2. The second tap has a shorter fence and longer combs. Its working diameter is intermediate between the diameters of the other tools in the set.
3. The third tap, with which the hole for cutting metric threads is processed last, is characterized by full ridges of cutting teeth and a diameter that must exactly match the size of the thread being formed.

Taps are used primarily for cutting metric threads. Much less often than metric ones, taps designed for processing the internal walls of pipes are used. In accordance with their purpose, they are called pipe, and they can be distinguished by the letter G present in their markings.

Internal thread cutting technology

As mentioned above, before starting work, you need to drill a hole, the diameter of which must exactly fit a thread of a certain size. It should be borne in mind: if the diameters of the holes intended for cutting metric threads are chosen incorrectly, this can lead not only to poor quality execution, but also to breakage of the tap.

Considering the fact that the tap, when forming threaded grooves, not only cuts the metal, but also pushes it, the diameter of the drill for making threads should be slightly smaller than its nominal diameter. For example, a drill for making M3 threads should have a diameter of 2.5 mm, for M4 - 3.3 mm, for M5 you should choose a drill with a diameter of 4.2 mm, for M6 threads - 5 mm, M8 - 6.7 mm, M10 - 8.5 mm, and for M12 - 10.2.

Table 1. Main diameters of holes for metric threads

All drill diameters for GOST threads is given in special tables. Such tables indicate the diameters of drills for making threads with both standard and reduced pitches, it should be borne in mind that holes are drilled for these purposes different diameters. In addition, if threads are cut in products made of brittle metals (such as cast iron), the diameter of the thread drill obtained from the table must be reduced by one tenth of a millimeter.

You can familiarize yourself with the provisions of GOST regulating the cutting of metric threads by downloading the document in pdf format from the link below.

The diameters of drills for metric threads can be calculated independently. From the diameter of the thread that needs to be cut, it is necessary to subtract the value of its pitch. The thread pitch itself, the size of which is used when performing such calculations, can be found out from special correspondence tables. In order to determine what diameter the hole needs to be made using a drill if a three-start tap is used for threading, you must use the following formula:

D o = D m x 0.8, Where:

Before- this is the diameter of the hole that must be made using a drill,

D m– the diameter of the tap that will be used to process the drilled element.

Making internal threads is usually not difficult. But there are some features of using the tool and selecting holes for cutting metric threads.

Types of thread

They differ in their main characteristics:

• diameter calculation system (inch, metric, others);
• number of passes (two-, three- or single-pass);
• profile shape (rectangular, trapezoidal, triangular, round);
• direction of rotation of the screw (left or right);
• placement on the part (internal or external);
• shape of the part (cone or cylinder);
• purpose (running, fastening and sealing or fastening).

According to the listed characteristics, the following types are distinguished:

• cylindrical (MJ);
• metric and conical (M, MK);
• pipe (G, R);
• Edison round (E);
• trapezoidal (Tr);
• round for plumbing fasteners (Kp);
• persistent (S, S45);
• inch, including cylindrical and conical (BSW, UTS, NPT);
• oil range.

Tools for internal threading

To make internal cutting, you need a tap - a screw-shaped tool with sharp grooves. The rod can be shaped like a cone or a cylinder. The grooves run lengthwise and break the thread into sections called combs. It is the edges of the combs that are the working surfaces.

To ensure a clean groove, the metal is removed gradually, in layers. This requires one very long tool or set.

Single taps are also found on sale; they are often used to correct broken threads. To cut a new one, buy a kit. Therefore, taps are usually sold in pairs: for roughing and for finishing work. The first one cuts a shallow groove, the second one cleans and deepens it. There are also three-pass tools. Thin taps, up to 3 millimeters, are sold in twos, wider ones - in threes. Three-pass taps are inserted into the gates. The design of the knobs is different, but their size must match the size of the cutter.

The tools in the set are distinguished by the marks marked on the tail end. If you look closely, you will notice differences in shape:

• the first tap has heavily cut tooth tips, the outer diameter is slightly smaller than the other tools in the set;
• second tap with shorter fence segment, longer ridges. Its diameter is slightly larger than that of the first;
• the third tap has full ridges of teeth, and its diameter should match the dimensions of the future thread.

Taps are divided into pipe taps (marked “G”) for cutting threads inside the pipe, and metric taps, which are more common.

The quality directly depends on the properties of the tap: it must be made of good metal and spicy. To extend the life of the tool and improve the quality of the thread, lubricant is used. Usually, to acquire a stable cutting skill, you need to make 3 - 5 attempts.

Cutting process

Before you start cutting, you should use drills to make a hole in the workpiece. The diameter of the hole from the drill must match internal size threads. When the size of the hole made with drills is chosen incorrectly, the tool can break or the grooves will turn out to be of poor quality.

During cutting, part of the metal does not fall out with chips, but is pressed along the working surfaces of the tap, forming a groove profile on the workpiece. Taking this feature into account, the size of the drill used to make the hole for the thread is selected slightly smaller than the nominal diameter of the future thread.

For example, when cutting M5 (groove diameter is 5 mm), you should choose a drill for a 4.2 mm hole. To cut M4, the diameter of the drill must be 3.3 millimeters, and before working with an M6 tap, a hole is first made with a 5 mm drill. This indicator is calculated taking into account the thread pitch. The pitch can be calculated mathematically, but in practice they resort to correspondence tables, where for an M5 tap the pitch is 0.8, for M4 this figure is 0.7, for M6 - 1. We subtract the pitch index from the diameter and get required diameter drill. When working with brittle metals, such as cast iron, the drill diameter should be reduced by 0.1 mm compared to the size recommended in the table.

The formula for calculating the hole diameter when working with three-pass taps:

Up=Dm * 0.8;

here: Dm is the diameter of the tap.

Type	Diameter	Step
M1	0,75	0,25
M1,2	0,95	0,25
1,4	1,1	0,3
1,7	1,3	0,36
2,6	1,6	0,4
2,8	1,9	0,4
M3	2,1	0,46
M3	2,5	0,5
M4	3,3	0,7
M5	4,1	0,8
M6	4,9	1
M8	6,7	1,25
M10	8,4	1,5

Table 1. Correspondence between thread diameters and preparation hole

Before starting work, the tap is inserted into a square shank - a knob. The collars can be regular or ratchet. The carving is done carefully, the first pass is made with a No. 1 tap to the end. Special attention it is necessary to pay attention to the direction of movement: clockwise only, and some force must be applied. It is done like this: 1/2 turns along the stroke alternate with 1/4 turns against the screw stroke to destroy the chips.

Thread in inches	External D, mm	Diameter, mm	Pitch, mm
1\8″	2,095	0,74	1,058
1\4″	6,35	4,72	1,27
3\16″	4,762	3,47	1,058
5\16″	7,938	6,13	1,411
7\16″	11,112	8,79	1,814
3\8″	9,525	7,49	1,588

Table 2. Hole diameters for inch threads

A couple drops of lubricant will make working on blind threaded holes much easier. Although sometimes used as a lubricant machine oil, drying oil is optimal for working with steel. WITH aluminum alloys It is preferable to use kerosene, alcohol or turpentine. Technical oil can also be used, but with less effect.

Homemade tap for aluminum alloys

To create internal threads in brass or light alloy parts, you can use homemade instrument and drills from the usual set. Calibrated steel wire will do. Using a die, an external thread is cut on it, after which the workpiece is hardened. After hardening, it is necessary to release the part to the color of ripe straw. Cutting edges are sharpened using a whetstone or sharpener, having previously clamped the part into a collet chuck.

Video on how internal threads are cut:

TAPPING HOLES
PIPE TAPER THREAD

DIAMETERS

GOST 21350-75

STATE COMMITTEE OF STANDARDS
COUNCIL OF MINISTERS OF THE USSR

Moscow

DEVELOPED, INTRODUCED AND PREPARED FOR APPROVAL by the All-Union Scientific Research Institute for Normalization in Mechanical Engineering (VNIINMASH)

And about. directors Gerasimov N.N.

Topic leader and performer Zaroslova M.P.

APPROVED AND ENTERED INTO EFFECT by Resolution State Committee standards of the Council of Ministers of the USSR dated December 12, 1975 No. 3877

STATE STANDARD OF THE USSR UNION

HOLES FOR TAPERED PIPE THREAD Diameters Holes for threading pipe taper screw thread. Diameters

GOST 21350-75 In return MN 5389-64

By Decree of the State Committee of Standards of the Council of Ministers of the USSR dated December 12, 1975 No. 3877, the validity period was established

from 01.01.77

1. This standard establishes the diameters of holes for cutting conical pipe threads in accordance with GOST 6211-69 in steel products in accordance with GOST 380-71, GOST 4543-71, GOST 1050-74, GOST 5058-75 and GOST 5632-72 (except for alloys on nickel base) and copper according to GOST 859-66.

2. The diameters of the holes with reaming to a cone and their maximum deviations must correspond to those indicated in the drawing. 1 and in table. 1.

Table 1

Dimensions in mm

Number of threads per 1²

Step R

Hole diameter

Drilling depthl

d c

d o

Nom.

Prev. off

Nom.

Prev. off

0,907

8,10

0,20

8,57

0,10

1,337

10,80

0,24

11,45

14,30

14,95

1,814

17,90

18,63

23,35

0,28

24,12

2,309

29,35

30,29

1 1/4

37,80

0,34

38,95

1 1/2

43,70

44,85

55,25

0,40

56,66

Note. For threads with nominal size above 2² nominal hole diametersd o and their maximum deviations must be equal to those established by GOST 6211-69 for the internal diameter of the thread.

3. The diameters of the holes without turning to a cone and their maximum deviations must correspond to those indicated in the drawing. 2 and in table. 2.

4. Allowed for pipe cutting tapered thread use holes of other diameters obtained on the basis of experimental data.

5. The diameters of drills for holes for tapping are indicated in the recommended one.

table 2

Dimensions in mm

Nominal thread size in inches

Number of threads per 1²

Step R

Hole diameterd c

Drilling depthl

Nom.

Prev. off

1 / 8

0,907

8,25

0,20

1 / 4

1,337

11,05

0,24

3 / 8

14,50

1 / 2

1,814

18,10

0,28

3 / 4

23,60

2,309

29,65

1 1 / 4

38,30

0,34

1 1 /2

44,20

56,00

0,40

Diameters of drills for holes for cutting conical pipe threads Dimensions in mm Nominal thread size in inches Number of threads per 1² Step R Drill diameter for hole with cone deployment without cone deployment 1 / 8 0,907 1 / 4 1,337 10,8 11,1 3 / 8 14,25 14,5 1 / 2 1,814 3 / 4 23,25 2,309 1 1 / 4 38,25 1 1 /2 56,00