Parts that have some kind of carving have been known since the time of the ancient Greek philosopher and mathematician Archimedes ( Ἀρχιμήδης - from ancient Greek “chief adviser”), who lived in Syracuse on the then Greek island of Sicily. Very rare, single bolts, similar to modern ones, are found in the design of door hinges in houses considered modern official history to Ancient Rome. This seems to be understandable, say modern historians and archaeological reconstructionists: forging or otherwise manually applying a screw thread to a part is extremely difficult and unreasonably labor-intensive - it is more practical to use rivets or gluing/welding/soldering. Actually, bolts and threaded screws identical to modern ones are found in antique mechanical watch complex and elegant design and in printing machines the origin of which is unknown for certain, but dated by official scientists to the 15th century, which is doubtful, since the watches have many very small screws that are almost impossible to make by hand, and the first thread-cutting machine, according to the same official historians, invented by the French craftsman Jacques Besson about 100 years later - in 1568. The machine was powered by a foot pedal. A thread was cut into the workpiece being processed using a cutter moved by a lead screw. The machine was designed to coordinate the translational movement of the cutter and the rotation of the workpiece, which was achieved using a pulley system. Only with its advent did it become convenient and possible to widely use “Bolt+Nut” detachable connections, the convenience of which lies in repeated assembly and disassembly without loss of functional qualities.

Since the end of the 18th century (it is not clear how it was even earlier), large threads were applied to parts using hot forging: blacksmiths hit the hot bolt blank with a special profile forging die, hammer or other special shaping tool. Cutting smaller threads was done on primitive lathes. In this case, the master had to hold the cutting tools manually, so it was not possible to obtain the same thread of a constant profile. As a result, the bolt and nut were made in pairs, and this nut would not fit with another bolt - such threaded connections were stored in a screwed state until the moment of their use.

The real breakthrough in the manufacture and use of threaded fasteners is associated with the Industrial Revolution, which began in the same last third of the 18th century in Great Britain. Characteristic feature The industrial revolution is the rapid growth of productive forces based on large-scale machine industry. A large number of machines required huge amount fasteners for their production. Many well-known technical inventions of that time were based on the use of threaded fasteners. Among them, invented by James Hargreaves spinning machine batch spinning and Eli Whitney cotton gin. Railways, which are growing at incredible speed, have also become huge consumers of threaded fasteners.

Since threaded parts were initially widely developed and widespread in Great Britain, the dimensions of thread parameters were forced to be used by engineer-inventors around the world, quite strange, and, it seems, borrowed from some earlier engineers, whose existence is obvious (magnificent the cathedrals still stand today), but are kept secret. They call the system anthropometric: the measure in it is a person, his legs, arms - which seems absurd: after all, all people are different - how to use such a system in the absence of an established production of measuring instruments? It seems that the authors of the explanation of the meaning of the English system of measures tried to link to the explanation the famous saying: “Man is the measure of everything” - one of the inscriptions on the facade at the entrance to the Temple of Apollo at Delphi.

Until the end of the 18th century, the North American United States were under the colonial rule of Great Britain and, therefore, also used the English system of measures.

The basic unit of the English system of measures is INCH . The official version of the origin of this unit of measurement and its name states that inch (from the Dutch word duim - thumb) - the width of the thumb of an adult man - again, funny: everyone’s fingers are different, but the name and surname of the standard man are not reported.

(official illustration - must be the hand of, to put it mildly, a rather large man)

According to another version, the inch comes from the Roman unit of measure ounce (uncia), which was simultaneously a unit of measurement of length, area, volume and weight. It is rather not a universal measure, but a fractional proportion of each of the unit measures, like half or a quarter. In each of these unit measures, the ounce was 1/12 of a larger unit of measurement: length (1/12 foot), area (1/12 juger), volume (1/12 sextarium), weight (1/12 libra). An ounce of a day is an hour, and an ounce of a year is a month.

It turns out that if an inch is 1/12 of a foot (translated from English as “foot”), then, based on today’s value of an inch, a foot should be about 30 cm long, and then an inch will be about 2.5 cm. And again: by whom was that standard guy with a “standard” foot? History is silent.

At some point it was recognized as the main English inch . Since many countries of the world were forced at the end of the 18th - beginning of the 19th centuries to submit to the Anglo-Dutch world rule, many countries imposed their own local “Inches”, each of which was slightly different in size from the English one (Viennese, Bavarian, Prussian, Courland , Riga, French, etc.). However, the most common has always been English inch , which over time practically replaced all others from use. To designate it, a double (sometimes a single) stroke is used, as in the designation of arc seconds ( ″ ), without a space after the numeric value, for example: 2 ″ (2 inches).

To date 1 English inch (hereinafter simply inch ) = 25.4 mm .

A critical problem that could not be solved in fasteners until the early 19th century was the lack of uniformity among the threads cut on bolts and nuts in different countries and even across countries. different factories within one country.

The aforementioned American inventor of the cotton gin, Eli Whitney, expressed another important idea - the interchangeability of parts in machines. He demonstrated the vital need to implement this idea in 1801 in Washington. Before the eyes of those present, among whom were President John Adams and Vice President Thomas Jefferson, Whitney laid out ten identical piles of musket parts on the table. Each pile contained ten parts. Taking one different part at random from each pile, Whitney quickly assembled one finished musket. The idea was so simple and convenient that it was soon adopted by many engineers and inventors around the world. In fact, all currently valid technical standards GOST, DSTU, DIN, ISO and others are based on this idea of ​​​​E. Whitney’s interchangeability.

At the same time, in England (Great Britain), which was in constant technical and technological competition with France, both directly and on the territory of its colonies, the idea had long been hatched to prevent in every possible way the advancement industrial development and the advancement of the French army in the event of a possible attack on England or the English colonies. Imposing on the French, and all other enemies of the British crown, some other (non-inch) system of measures in the manufacture of machine parts and mechanisms, including fasteners, would allow England to “put a spoke in the wheels” of the worldwide spread of the newly adopted system of inch interchangeability and significantly restrain technical and technological development France and its other global competitors; make it impossible to repair and assemble English equipment and weapons using French or other non-English spare parts. The implementation of this plan became possible after the organization of the Great French Revolution under the direct leadership of the British station in France. One of the results of the Great French Revolution was the rapid introduction of a new metric system of measures, which became widespread at the end of the 18th and beginning of the 19th centuries in France. In Russia, the metric system of measures was introduced through the efforts of Dmitry Ivanovich Mendeleev, who replaced the “Depot of Exemplary Weights and Scales of the Russian Empire” with the “Main Chamber of Weights and Measures,” thus removing the old Russian measures from general circulation. And the metric system became widespread in Russia - and this can be considered just a coincidence - as in France, after the October Revolution.

The basis of the metric system is METER (it is believed that from the Greek "m" E tro" - measure). In drawings, documentation and designations of threaded products, it is customary to give all dimensions in millimeters (mm).

The authors of the new system of measures agreed that 1 meter = 1000 mm .

Subsequently, Napoleon, who united almost all of Europe, managed to spread the metric system in his subordinate countries. Napoleon did not capture Great Britain, and the British continue to use the inch system of measures, alien to other Europeans, thus dividing the spheres of influence and protectorate in the technical and technological structure of the world community. The Americans (also former British) take the same position. The Americans and the British themselves call their system of measures “Imperial”, and not at all “inch”, as we call it. Together with the Americans, the “imperial” system of measures is also used by other “British colonial states”: Japan, Canada, Australia, New Zealand, etc. So, the British Empire disappeared only geographically, and today the provinces of the Empire continue to use the “imperial” system of measures, and The Empire's cryptocolonies use the metric system.

The metric system of measures was created by the leading minds of the time, gathered under the banner of the Great French Revolution (we all knew from school the scientists of the French Academy of Sciences: Charles Augustin de Coulon, Joseph Louis Lagrange, Pierre-Simon Laplace, Gaspard Monge, Jean-Charles de Bordes, etc. .), therefore everything in this system was built simply, logically, conveniently and subordinated to whole round numbers. Well, perhaps the division of time into seconds, minutes and hours, which we inherited from the ancient Sumerians with their sexagesimal number system, introduces some inconsistency into the metric system of measures. Or, for example, dividing a circle into 360 degrees. Echoes of the Sumerian number system were preserved in the division of the day into 24 hours, the year into 12 months, and in the existence of a dozen as a measure of quantity, as well as in the division of a foot into 12 inches, since the inch system of measures was based on the much more ancient Sumerian one.

No matter how hard the mathematician-engineer Jean-Charles de Bordes fought with other academicians for the logical beauty of numbers, so that there were 100 seconds in a minute, 100 minutes in an hour, and 10 hours in a day (they even managed to introduce a new time system), but in the end , nothing came of it. An amazing watch with a two-standard transition dial is shown in the photo.

It seems quite logical to create the simplest size range of metric threads with a pitch of, say, 5 mm: ... M5; M10; M15; M20...M40...M50...etc. But! Since the machines and mechanisms that already existed at the time of the creation of the metric system of measures were tied in their dimensions and configuration to inch dimensions, this necessitated the need to adapt to the existing connecting dimensions and dimensions. This is where, at first glance, “strange” thread sizes appear: M12 (which is practically 1/2" - half an inch), M24 (replaces a 1" thread), M36 (which is 1 1/2" - one and a half inches), etc. d.

International classification of threads

To date, the following main international thread standards have been adopted (the list is far from complete - there are also a large number of non-basic and special thread standards that are internationally accepted for use):

Currently, the most widespread in foreign technology is thread standard metric ISO DIN 13:1988 (first line in the table) - we also use this standard ( GOST 24705-2004 And DSTU GOST 16093:2018 on metric threads are his own sons). However, other standards are used around the world.

The reasons why international thread standards differ are already described above. It can also be added that some thread standards are special, and the use of such threads is limited to the scope of application of parts with this thread (for example, pipe thread, invented by the English engineer-inventor Whitworth, BSP used only in pipe connection parts).

Metric cylindrical thread

There are different metric threads used for fasteners, but the most common are metric cylindrical threads (i.e. the threaded part has a cylindrical shape and the diameter of the thread does not change along the length of the part) with a triangular profile with a profile angle of 60 0

Further we will talk only about the most common metric thread - cylindrical. In metric cylindrical threads, the designation of the thread size of the screwed parts is taken outside diameter bolt threads. It is difficult to accurately measure the thread of the nut. In order to find out the thread diameter of a nut, it is necessary to measure the outer diameter of the bolt corresponding to this nut (on which it is screwed).

M ― outer diameter of the bolt (nut) thread ― designation of the thread size

N - height of the metric thread profile, Н=0.866025404×Р

R — thread pitch (distance between the vertices of the thread profile)

d CP - average thread diameter

d VN - internal diameter of the nut thread

dB - internal diameter of the bolt thread

Metric thread is designated by a Latin letter M . The carving can be large, small and especially small. Large threads are accepted as normal:

• if the thread pitch is large, then the pitch size is not written: M2; M16 - for nut; M24x90; M90x850 - for bolt;
• if the thread pitch is small, then the pitch size is written in the designation using the symbol X: M8x1; M16x1.5 - for nut; M20x1.5x65; M42x2x330 - for bolt;

Metric cylindrical threads can have a right or left direction. The right direction is considered basic: it is not indicated by default. If the thread direction is left, then the symbol is placed after the designation L.H. : M16LH; M22x1.5LH - for nut; М27х2LHх400; M36LHx220 - for bolt;

Accuracy and tolerance range of metric threads

Metric cylindrical threads vary in manufacturing accuracy and are divided into accuracy classes. The accuracy classes and tolerance ranges of metric cylindrical threads are given in the table:

The most common accuracy class is medium with thread tolerance fields: 6g - for a bolt (screw, stud) and 6N - for a nut; Such tolerances are easily maintained in production when making threads using the rolling method on thread rolling machines. Indicated by a dash after the thread size: M8-6gx20; M20x1.5-6gx55 - for bolt; M10-6N; М30х2LH-6Н - for nut.

Diameters and pitches of metric threads

All diameters of metric threads are divided into three conventional rows according to the degree of preference and applicability (see table below): the most common threads are from the 1st row, the least recommended for use are metric threads from the 3rd row (they have a very narrow area of ​​​​use and rarely found in mechanical engineering). Thus, in order to maximally avoid problems with fastening threaded components during assembly, operation and subsequent repairs, design engineers are recommended to include threads from the 1st row in the design of machines and mechanisms. Also, each diameter of a metric thread corresponds to several steps: large - the main step for application; fine - an additional step for adjustment and high-strength fasteners; especially small - least recommended for use. In turn, the tool industry produces the largest quantities of thread-cutting tools for metric threads from the 1st row with a large thread pitch. And the most difficult to find, sometimes almost exclusive and expensive, are thread-cutting tools for threading from the 3rd row with fine and especially fine pitches.

How to determine metric thread pitch

• The easiest way is to measure the length of ten turns and divide by 10.

• You can use a special tool - a metric thread gauge.

The following table provides a list of metric thread diameters and the corresponding thread pitches for each diameter.

Inch threads

As mentioned earlier, the birthplace of standardized carving can be considered Great Britain with its English system of measures. The most prominent English engineer-inventor who was concerned with putting threaded parts in order was Joseph Whitworth ( Joseph Whitworth ), or Joseph Whitworth, that’s also correct. Whitworth turned out to be a talented and very active engineer; so active and enterprising that the first thread standard he developed in 1841 B.S.W. was approved for general use at the state level in 1881. At this point the carving B.S.W. has become the most common inch thread not only in Great Britain, but also in Europe. The prolific J. Whitworth developed a number of other standards for inch threads for special applications; some of them are still widely used today.

At first the carving B.S.W. found application in the United States of America. However, intensive industrialization in the United States required a lot of threaded fasteners, and Whitworth threads were technically difficult to mass produce, as were the metal-cutting tools for them. In 1864, the American industrialist and manufacturer of metal-cutting tools and fasteners, William Sellers, proposed simplifying threads. B.S.W. by changing the angle and shape of the thread profile, which led to cheaper and easier production of threaded fasteners. The Franklin Institute adopted the W. Sellers system and recommended it as state standard. By the end of the 19th century, American inch threads spread to Europe, and even partially replaced English threads, due to the lower cost of fastener production. The incompatibility of the Whitworth and Sellers threads caused many technical complications in the early twentieth century. As a result, in 1948, the International Unified System of Inch Threads was adopted and approved, which included elements of both Whitworth and Sellers threads - the most basic inch threads of this system UNC And UNF are still relevant today.

How to deal with inch threads

For a person brought up in the metric system of measures, the easiest way to understand inch threads is to measure the outer diameter of the thread, the inner diameter and the pitch of the thread (measured in the number of threads per inch) with a caliper in millimeters. It is necessary to measure with an accuracy of tenths and hundredths of a millimeter. Then you need to use the reference tables of inch threads (the main ones are given below) to select a match for the resulting combination. In this way, if you have reference tables and a caliper, you can easily figure out the identification of one or another inch fastener, both nuts and bolts, screws.

How to determine the pitch of an inch thread

As we already know, 1 inch is quite inconvenient and relatively large. Therefore, Sir Joseph Whitworth found it difficult to accurately measure the distance between the tops of a thread in fractions of an inch (as we do with metric threads), and he decided that the simplest and most accurate parameter for the thread pitch would not be the distance between the tops of the profile, but the number of turns thread, which fits into 1 inch of thread length - the turns can even be counted visually.

This is how the pitch of any inch thread is determined to this day - in the number of turns per inch.

• This means that the first method is to attach an inch ruler to the thread (an ordinary metric ruler with a mark of 25.4 mm will do) and count the number of turns that fit in 1 inch (25.4 mm). The example shows an inch thread with a pitch of 18 threads per inch.

• the second method - you can use a special tool - a thread gauge for inch threads (however, you need to know what inch thread you are going to measure, since English and American inch threads differ in the angle of the thread profile: 55° and 60°)

Inch English Whitworth Straight Thread BSW (British Standard Whitworth)

This is a cylindrical inch thread with a large pitch, provided by J. Whitworth for general use. J. Whitworth's idea was that he proposed once and for all to secure strictly defined thread parameters for bolts and screws of the same type and size: profile, pitch and height of the thread profile. Based on his own experience and conclusions, J. Whitworth insisted that the thread profile angle (the angle between the sides of adjacent turns) be equal to 55°. The tops of the threads and the bases of the thread valleys should be rounded to 1/6 the height of the original profile - thus Whitworth wanted to achieve tightness (tightness) of the thread and increase its strength by increasing the contact area of ​​​​the bolt and nut. The thread pitch should be determined by the number of threads per inch of thread length; in this case, the number of thread turns per 1 inch should not be constant for all thread diameters, but should depend on the thread diameter of the bolt or screw: the smaller the diameter, the more thread turns per inch; the larger the thread diameter, the correspondingly smaller the number of threads per inch of thread length.

W , followed by the size of the outer diameter of the bolt, measured in inches:

• nut designation: W 1/4" (one-fourth inch Whitworth thread nut);
• bolt (screw) designation: W 3/4" X 1 1/2” (three-quarters inch Whitworth bolt, one and a half inches long).

B.S.W. "Drilling diameter, mm"

Despite the fact that all provinces of the British Empire have long been using a unified inch thread UNC replaced B.S.W. in the metropolis, the British have not abandoned the outdated Whitworth carving to this day.

Inch English Straight Fine Thread Whitworth BSF (British Standard Whitworth Fine Thread)

Inch cylindrical fine thread BSF was very common until the 50s of the twentieth century, along with carving B.S.W. . Used for the manufacture of precise and high-strength fasteners. Subsequently, it was replaced by a unified inch fine thread UNF. Although the British use carvings BSF and in our time.

Indicated by Latin letters BSF , followed by the size of the outer diameter of the bolt, measured in inches:

• nut designation: BSF 1/4" (one-fourth inch Whitworth inch fine thread nut);
• bolt (screw) designation: BSF 3/4" X 1 1/2” (Three quarter inch Whitworth thread bolt, one and a half inches long).

Parameters in millimeters of thread BSF are given in the following table (for nuts - see column "Drilling diameter, mm"- this is the diameter of the inner hole of the nut for threading).

Inch English Cylindrical Non-Self-Sealing Whitworth Pipe Thread BSP (British Standard Whitworth Pipe Thread)

It is worth mentioning the Whitworth pipe thread, since from the moment of its invention to the present day it has been widely used throughout the world for parts of threaded connections of pipelines: bends, transitions, fittings, couplings, doubles, tees, etc.; as well as for pipeline fittings: taps, valves, etc.

In the post-Soviet space, the Whitworth cylindrical pipe thread standard, adapted by Soviet engineers, is in effect. BSP - this is a carving GOST 6357-81 .

Denoted by a Latin letter G , after which the numerical value of the nominal diameter of the pipe in inches is placed (this number is neither the outer nor the inner diameter of the thread or pipe):

• lock nut designation: G 1/4" (lock nut with an inch Whitworth straight pipe thread for a pipe with a nominal bore diameter of one fourth inch); The same lock nut in domestic mechanical engineering is designated: Du8 (lock nut for pipe with nominal bore 8 mm)

Here it is necessary to clarify the situation with the designation of the pipe thread size BSP. Pipes are designated by "nominal pipe bore" or "nominal pipe diameter", which are loosely related to the actual actual dimensions of the pipe. For example, let's take steel pipe 2" (two inches): having measured its internal diameter and converted it into inches, we are surprised to find out that it is about 2⅛ inches, and its outer diameter will be about 2⅝ inches - such an absurdity!

How to determine the actual diameter of a pipe?

Unfortunately, there is no formula for converting "pipe inches" to millimeters or to "regular" inches to determine the actual outside or inside diameter of a pipe. To determine the compliance of the “conventional inch diameter”, “outer diameter of the pipe” and “pipe thread diameter”, it is necessary to use reference literature and regulatory documentation (standards).

Below is a table that was compiled by combining known standards together (it may not be complete, but it can help with determining pipe threads BSP; for locknuts - see column "Drilling diameter, mm"- this is the diameter of the inner hole of the nut for threading)

Inch Unified Parallel Coarse Thread UNC (Unified National Coarse Thread)

Parallel inch thread UNC , in its final form, was developed by the American National Standards Institute ( ANSI/ISO ) and became the international standard for inch threads with large pitches, and, in fact, represents the embodiment of the technical ideas of the American industrialist Sellers to improve the Whitworth thread. The improvements essentially boiled down to changing the profile angle from the awkward 55° to 60° and eliminating the roundings at the tops of the thread profile - now the surface of the tops has become flat and is 1/8 of the thread pitch. The depressions can also be flat, but rounded ones are preferable.

Thread UNC is currently the most common inch thread in the world and is recommended as the preferred thread for use.

Accepted designation for inch coarse threads UNC includes a letter indication of the thread type (actually UNC ) and nominal thread diameter in inches. Additionally, the designation may include: thread pitch, indicated by a dash ( TPI ― threads per inch ― threads per inch ), direction (left or right). Inch large threads UNC sizes smaller than 1/4”, due to difficulties in measuring them, are usually designated by numbers from No. 1 to No. 12, indicating the thread pitch through a dash, measured in the number of turns per inch.

1/4” – 20UNСх2 1/2”

• UNС - thread type ― unified inch thread with large pitch
• 1/4” UNС 6.35 mm 5.35 mm )
• 20
• 2 1/2” 63.5 mm )

Parameters in millimeters of thread UNC are given in the following table (for nuts - see column "Drilling diameter, mm"- this is the diameter of the inner hole of the nut for threading).

Inch unified cylindrical fine thread UNF (Unified National Fine Thread)

Thread UNF ― cylindrical inch thread with fine pitch, used for adjustment and high-strength fasteners.

Thread UNF , along with carving UNC is currently the most common inch thread in the world and is also recommended as preferred for applications where a finer thread pitch is required.

Designation of inch fine thread UNF similar to thread designation UNC and also includes the letter designation of the thread type and the nominal diameter in inches. Additionally, the designation may include: thread pitch, indicated by a dash ( TPI ― threads per inch ― threads per inch ), direction (left, right). Threads UNF sizes smaller than 1/4”, due to difficulties in measuring them, are usually designated by numbers, from No. 0 to No. 12, indicating the thread pitch through a dash in the number of turns per inch.

For example: Designation of a bolt with an inch thread 1/4” – 28UNFx2 1/2”

• UNF - thread type ― unified inch thread with fine pitch
• 1/4” - designation of thread diameter (according to the thread table UNF given below, for a bolt the outer diameter of the thread corresponds to 6.35 mm , for a nut - the diameter of the hole inside the nut corresponds to 5.5 mm )
• 28 - thread pitch, measured in the number of turns per inch of thread length (the number of turns that fit in 25.4 mm)
• 2 1/2” - bolt length in inches (approximately corresponds to 63.5 mm )

Parameters in millimeters of thread UNF are given in the following table (for nuts - see column "Drilling diameter, mm"- this is the diameter of the inner hole of the nut for threading).

Inch unified cylindrical extra fine thread UNEF (Unified National Extra Fine Thread)

Thread UNEF - cylindrical inch thread with particularly fine pitch, used for high-precision fasteners and threaded parts of precision mechanisms - special inch thread.

Designated similarly to threads UNF And UNC .

Parameters in millimeters of thread UNEF are given in the following table (for nuts - see column "Drilling diameter, mm"- this is the diameter of the inner hole of the nut for threading).

There are also other standards for inch threads, but they are special, highly specialized, rarely used and are not recommended for use, so we will not present them.

A thread is an ornate spiral with a constant pitch applied to a conical or cylindrical surface. It is the main element for connecting two types of fasteners, as well as screw and gear-screw gears. The main parameters of threads on modern ones are defined in GOST 11708-82: these are between adjacent turns, the outer and inner diameters of the fastener element, the angle of the top of the thread.

Types of threads on fasteners are divided into:

• internal - applied to nuts, anchor sleeves, couplings, pipes;
• external - located on self-tapping screws, screws, studs.

There are the following types of threads according to the relevant GOST:

• metric - profile in the form of an equilateral triangle (available in small, medium and large steps);
• inch - triangular or trapezoidal;
• metric conical - has a triangular profile;
• round - a protrusion of the top of a round shape;
• trapezoidal - a protrusion of the top of a trapezoidal shape;
• persistent - trapezoidal asymmetrical profile;
• modular - trapezoidal profile shape;
• pipe conical and cylindrical (the profile has the form of an inch-sized isosceles triangle with a rounded (or flat-cut) top and a hollow of the coil);
• conical inch - a profile with a flat-cut triangular top.

There are also types of threads such as square and rectangular. They are applied to fasteners using screw-cutting lathes according to individual drawings. These types of threads do not allow for high precision, so they are used quite rarely. There are no GOST standards for them.

Today, for general engineering applications, the main external and internal threads are considered to be metric. In the drawings it is indicated capital letter"M" indicating the outer diameter in millimeters. Pipe threads are used to connect various pipes. Their nominal diameter is the inner outside of which In the drawings it is designated by a large letter “G” indicating the inner diameter of the pipe in inches.

The main thread sizes of all types are reference data. They can be found in any machine builder's reference book. For metric threads, reference data is described in detail according to GOSTs 9150-81, 24705-81 and 8724-81. For cylindrical pipe threads, the dimensions are specified in GOST 6357-81.

One common fastener with metric threads is a bolt. It is a metal rod with a head at the end. A helical groove is applied along the length of the rod. The purpose of bolts is to connect various parts of mechanisms and structures using a nut. The bolt head can be hexagonal or shaped (countersunk, semicircular, butt, embedded, terminal).

There are the following types of bolts according to their intended purpose:

• furniture - used for connecting products in furniture production;
• mechanical engineering - used in industrial sectors;
• plowshares - designed for coupling equipment of machines in the agricultural industry;
• road - used to connect various metal structures and

Wood carving [Techniques, techniques, products] Podolsky Yuri Fedorovich

Types of wood carving

Types of wood carving