Thread

• Unit of diameter (metric, inch, modular, pitch thread)
• Surface location (male and female)
• The direction of movement of the screw surface (right, left)
• The number of approaches (single and multiple), for example, two-way, three-way, etc.
• Profile (triangular, trapezoidal, rectangular, round, etc.)
• The forming surface on which the thread is located (cylindrical thread and tapered thread)
• Appointment (fixing, fixing and sealing, running, etc.)

Diameter Units

Scheme of cylindrical thread.

Conical thread pattern.

• Metric thread - in increments and basic thread parameters in millimeters.
• Inch thread - all thread parameters are expressed in inches (″), thread pitch in fractions of an inch . For an inch pipe thread, the size in inches characterizes conditionally the clearance in the pipe, and the outer diameter is actually substantially larger. Metric and inch threads are used in threaded connections and screw gears.
• Modular thread - thread pitch is measured by module (m). To get the size in millimeters, just multiply the module by the number pi (${\displaystyle \mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">\pi </span></span>}}$ {\ displaystyle \ pi}   )
• Pitch thread ^{[ unknown term ]} - thread pitch is measured in pitches ^{[ unknown term ]} (p). To get a numerical value (in inches), the number pi (${\displaystyle \mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">\pi </span></span>}}$ {\ displaystyle \ pi}   ) divided by pitch. Modular and pitch threads are used when cutting a worm gear. The profile of a turn of a modular worm can take the form of an Archimedean spiral , involute of a circle , elongated or shortened involute and trapezoid .

Main thread parameters

• Pitch (P) - the distance between the same sides of the profile, measured in fractions of a meter, in fractions of an inch or the number of threads per inch - this is the denominator of an ordinary fraction, the numerator of which is an inch. It is expressed as a natural number (for example: 28, 19, 14, 11).
• Outer diameter (D, d), diameter of the cylinder described around the peaks of the external (d) or hollows of the internal thread (D). It is equal to the diameter of the bolt blank before threading.
• The average diameter (D ₂ , d ₂ ), the diameter of the cylinder, the generatrix of which intersects the thread profile in such a way that its segments formed at the intersection with the groove are equal to half the nominal thread pitch.
• The inner diameter (D ₁ , d ₁ ), the diameter of the cylinder inscribed in the hollows of the external (d ₁ ) or the top of the internal thread (D ₁ ). It is equal to the diameter of the hole in the nut blank before threading:

• Stroke (P _h ) - distance along a line parallel to the axis of the thread, between any initial midpoint on the side of the thread and the midpoint obtained by moving the original midpoint along a helical line through an angle of 360 °, or - a value relative to the axial movement of the part with thread for one revolution. In single-start threading, the stroke is equal to the step, in multi-start threading is the product of step P by the number of entries n ^[2] :

• The height of the original thread triangle (H).
• Thread cut (s).
• Tapered thread cone angle (${\displaystyle \mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">\varphi </span></span>}}$ {\ displaystyle \ phi}   )
• Thread Angle (${\displaystyle \mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">\psi </span></span>}}$ {\ displaystyle \ psi}   ):

Metric (M)

It is widely used with a nominal diameter of 1 to 600 mm and a pitch of 0.25 to 6 mm. The profile is an equilateral triangle (angle at the apex of 60 °) with the theoretical profile height H = 0.866025404P. All profile parameters are measured in mm.

Standards:

• GOST 24705-2004 (ISO 724: 1993) “Metric thread. The main dimensions ";
• GOST 9150-2002 “Basic Interchangeability Standards. Thread metric. Profile";
• GOST 8724-2002 “Basic norms of interchangeability. Thread metric. Diameters and steps ";
• ISO 965-1: 1998 "General Purpose Metric Threads ISO. Tolerances. Part 1. Principles and main characteristics ”;
• ISO 965-2: 1998 "General Purpose Metric Threads ISO. Tolerances. Part 2. Limit sizes of threads for general purpose bolts and nuts. Middle accuracy class ";
• ISO 965-3: 1998 "General Purpose Metric Threads ISO. Tolerances. Part 3. Deviations for structural thread ";
• ISO 965-4: 1998 "General Purpose Metric Threads ISO. Tolerances. Part 4. Limit sizes for external screw threads, hot dip galvanized, for assembly with internal screw threads, cut with a tap from the tolerance position H or G after galvanization ";
• ISO 965-5: 1998 "General purpose metric threads. Tolerances. Part 5. Limit sizes for internal screw threads of screws for assembly with external screw threads, hot dip galvanized, with a maximum size of tolerance position h before galvanization ”;
• ISO 68-1 "General Purpose Screw Threads ISO. The main profile. Metric thread ";
• ISO 261: 1998, ISO Metric Threads for General Purpose. General form";
• ISO 262: 1998 “ISO Metric Threads for General Purpose. Selected sizes for screws, bolts and nuts ”;
• BS 3643 "ISO metric screw threads";
• DIN 13-12-1988 “Threads metric ISO basic and precision with a diameter of 1 to 300 mm. The choice of diameters and steps ";
• ANSI B1.13M, ANSI B1.18M "Metric M thread with profile based on ISO 68".

Symbols in thread markings: letter M (metric), numerical value of the nominal diameter of the thread (d, D in the diagram, it is the external diameter of the thread on the bolt) in mm, numerical value of the pitch (for threads with a small pitch) (P in the diagram) and the letters LH for left-hand thread. For example, a thread with a nominal diameter of 16 mm with a large pitch is designated as M16; thread with a nominal diameter of 36 with a fine pitch of 1.5 mm - M36 × 1.5; the same diameter and pitch, but the left thread is M36 × 1.5LH. These parameters can be applied to the tool in different places and not have the designation M, so the numbers 36 and 1.5, applied in different places, indicate M36 × 1.5. Also on the Soviet and Russian instruments, abbreviated marking of small steps is often found, for example, 2M16 or 1M16, which means "M16, small, second" or "M16, small, first," respectively. In this case, 1M means the first step from the main, 2M - the second. For this example, 1M16 means M16 × 1.75, and 2M16 means M16 × 1.5, since the main pitch of M16 is 2 mm.

Metric Conical (MK)

The taper is 1:16 (the cone angle is φ = 3 ° 34′48 ″). Designed to ensure tightness and locking of the thread without the use of additional tools. There are two versions of a threaded conical connection: a conical external thread with a conical internal thread and a conical external thread with a cylindrical internal thread.

Standard: GOST 25229-82 “Basic norms of interchangeability. Conical metric thread. "

Legend: letters MK, numerical value of the nominal diameter of the thread in mm, numerical value of the pitch, letters LH for the left thread. For example, threads with a nominal diameter of 24 mm in increments of 1.5 mm are designated as MK 24 × 1.5.

Cylindrical (MJ)

The cylindrical thread is based on a metric thread (M) with a nominal diameter of 1.6 to 200 mm and a profile angle of 60 ° at the top, designed for aerospace engineering and other applications requiring high fatigue strength and heat resistance . To ensure these properties, the thread cavity on the external thread has an increased radius from 0.15011P to 0.180424P. The internal thread MJ is compatible with the external thread M with the same nominal diameter and pitch.

Standards:

• GOST 30892-2002 (ISO 5855-1-99, ISO 5855-2-99, ISO 5855-3-99) “Metric thread with MJ profile. Profile, diameters and steps, tolerances ”;
• ISO 5855-1: 1999 "Aerospace - MJ threads - Part 1: General requirements";
• ISO 5855-2: 1999 "Aerospace - MJ threads - Part 2: Limit dimensions for bolts and nuts";
• ISO 5855-3: 1999 "Aerospace - MJ threads - Part 3: Limit dimensions for fittings for fluid systems";
• ANSI / ASME B1.21M-1997 (R2003) "Metric Screw Threads - MJ Profile".

Legend: letters MJ, numerical value of the nominal diameter of the thread in mm, numerical value of the pitch, tolerance field of the average diameter and tolerance field of the diameter of the protrusions. For example, an external thread with a nominal diameter of 6 mm, a pitch of 1 mm, a tolerance field of an average diameter of 4h and a tolerance field of the diameter of the protrusions 6h is indicated as MJ6 × 1-4h6h on the shaft surface.

Pipe Cylinder (G)

The inch thread is based on the BSW thread (British Standard Whitworth) and corresponds to the BSP thread (British standard pipe thread), has four pitch values ​​- 28, 19, 14 and 11 threads per inch. The profile angle at the apex is 55 °, the theoretical profile height is H = 0.960491P.

Standards:

• GOST 6357-81 “Basic Interchangeability Standards. Cylindrical pipe thread ";
• ISO R228;
• EN 10226;
• DIN 259
• BS 2779;
• JIS B 0202.

Legend: the letter G, the numerical value of the nominal pipe bore in inches, the accuracy class of the average diameter (A, B), and the letters LH for the left thread. For example, a thread with a nominal diameter of 1 1/8 ″ of accuracy class A is designated as G1 1/8-A. On many dies and klopp the letter G is omitted, respectively, any fractional designation is read exactly as a thread G. The nominal size of the thread corresponds to the clearance of the pipe in inches; the outer diameter of the pipe is in some proportion with this size.

Pipe conical (R)

Inch thread with a taper of 1:16 (cone angle - φ = 3 ° 34′48 ″). The profile angle at the apex is 55 °, the theoretical profile height is H = 0.960491P.

Standards:

• GOST 6211-81 "The basic norms of interchangeability. Conical pipe thread ";
• ISO R7;
• DIN 2999;
• BS 21;
• JIS B 0203.

Designation: letter R for external thread and Rc for internal, numerical value of nominal diameter of a thread in inches, letters LH for left-hand thread. For example, a thread with a nominal diameter of 1 1/4 ″ is designated as R1 1/4 ″.

Round for sanitary fittings (Cr)

The profile of a round thread is formed by circles, on tops and troughs, connected by straight lines with a profile angle at an apex of 30 °. Threads are used for spindles, valves, faucets, toilet and water taps.

Standard: GOST 13536-68 "Round thread for sanitary fittings. Profile, main dimensions, tolerances. ”

Designation of a round thread: letters Кр, nominal diameter of a thread, pitch and designation of a standard.

Keystone (Tr)

It is designed to transmit movement (leadscrews, caliper screws, control screws, cargo screws, etc.) and finds its application in various mechanical devices - lathes, car lifts, etc.

Metric thread with a profile angle at the apex of 30 °, theoretical profile height - H = 1.866P.

Standards:

• GOST 9484-81 “Basic norms of interchangeability. Trapezoidal thread. Profiles ";
• GOST 24737-81 “Basic Interchangeability Standards. Single trapezoidal thread. The main dimensions ";
• GOST 24738-81 “Basic Interchangeability Standards. Single trapezoidal thread. Diameters and steps ";
• GOST 24739-81 “Basic Interchangeability Standards. Multi-start trapezoidal thread. "

Designation of single-thread: the letter Tr (trapezoidal), the numerical value of the nominal diameter of the thread in mm, the numerical value of the pitch, the letters LH for the left thread and the designation of the tolerance field. For example, a single-thread external thread with a nominal diameter of 50 mm in increments of 8 mm is designated as Tr50x8-7e; the same diameter and pitch, but the left thread is Tr50 × 8LH-7e.

Thrust (S)

Resistant or sawtooth thread is a cargo thread. This thread finds application in mechanisms with large one-way pressure, such as, for example, in hydraulic presses, screw presses, press screws of rolling mills, in hook threads, artillery systems, etc. This is a metric thread with a side angle of 30 ° and 3 °.

Standard: GOST 10177-82 “Basic norms of interchangeability. The thread is resistant. Profile and main dimensions. ”

The symbol of the thread: the letter S, the numerical value of the nominal diameter of the thread in mm, the numerical value of the pitch, the letters LH for the left thread and the designation of the tolerance field. Multiple thread symbol: letter S, numerical value of the nominal diameter of the thread in mm, numerical value of the stroke, in brackets P with the numerical value of the pitch, the letters LH for the left thread and the designation of the tolerance field.

Thrust reinforced (S45 °)

Thread with an angle of inclination of the sides of the profile 45 ° and 3 °, with a nominal diameter of 80 to 2000 mm.

Standard: GOST 13535-87 “Basic Interchangeability Standards. Reinforced thread 45 degrees. "

The symbol of the thread: letter S, angle value 45 °, numerical value of the nominal diameter of the thread in mm, numerical value of the pitch, the letters LH for the left thread and designation TT.

Edison's Round (E)

It is used for electrical products, for example, the base of incandescent lamps ( Edison's base ).

Standard: GOST 6042-83 “Edison's thread is round. Profiles, sizes and size limits. ”

The symbol of the thread: letter E, thread number, if the thread is for non-metallic elements, letter N through the slash (/) and GOST number, for example, E27 GOST 6042-83 or E27 / N GOST 6042-83.

Metric (EG-M)

ISO metric thread for threaded bushings and wire threaded inserts. It is used as an enhancement of the bearing capacity of a thread or for repairing damaged threads in a part’s body ^{[3] [4]} .

Inch Cylinder (UTS: UNC, UNF, UNEF, 8UN, UNS)

Unified Thread Standard (UTS) - inch cylindrical thread, widely distributed in the USA and Canada. The angle at the apex is 60 °, the theoretical height of the profile is H = 0.866025P. It is divided into UNC (Unified Coarse), UNF (Unified Fine), UNEF (Unified Extra Fine), 8UN and UNS (Unified Special) depending on the step ^[5] .

UNC 1/4 (1/4 ″ × 1.27 mm) is extremely widespread , which is present in the mount of almost all digital and film cameras and camcorders, as well as small format tripods. Its parameters: D = 6.35 mm, D ₁ = 4.975 mm, pitch - 20 threads per inch (1.27 mm). Before it, 3/8 ″ thread with a pitch of 16 threads per inch (1.5875 mm), D = 9.525 mm and D ₁ = 7.806 mm was equally popular for mounting photographic equipment.

Standard: GOST 3362-75 “Photo and movie cameras. Tripod connection. The connecting sizes ".

Inch (BSW)

British Standard Whitworth (BSW) is a British inch thread proposed by Joseph Whitworth in 1841. The angle at the apex is 55 °, the theoretical height of the profile is H = 0.960491P. Fine pitch threads are called British Standard Fine (BSF).

Inch Conical (NPT)

National pipe thread (NPT) - ANSI / ASME standard inch cone thread (NPT) with a taper of 1:16 (cone angle - φ = 3 ° 34′48 ″) or cylindrical (NPS). The angle of the profile at the apex is 60 °, the theoretical height of the profile is H = 0.866025P.

The standard provides thread sizes from 1/16 ″ to 24 ″ for pipes.

Standards:

• GOST 6111-52 "inch conical thread with a profile angle of 60 degrees";
• ANSI / ASME B36.10M;
• BS 1600;
• BS EN 10255;
• ISO 65.

An example of a symbol for a 3/4 ″ tapered thread: K 3/4 ″ GOST 6111-52.

Oil Thread Threads

Oil threads are designed to connect pipes in oil wells. They are tapered for high tightness. According to the shape of the profile there are: triangular with a profile angle of 60 ° and trapezoidal unequal with angles from 5 ° to 60 ° (the so-called Butress thread). Oil threads are generally manufactured in accordance with American Petroleum Institute (API) standards.

Standards:

• GOST R 53366-2009 “Steel pipes used as casing or tubing for wells in the oil and gas industry. General specifications ";
• GOST 631-65 "Drill pipes with upset ends and couplings to them";
• GOST 632-80 "Casing pipes and couplings to them";
• GOST 633-80 "Tubing and couplings to them."

The following methods for producing threads are used:

• blade cutting ;
• abrasive treatment;
• rolling ;
• extrusion by pressing;
• casting ;
• electrophysical and electrochemical processing.

The most common and universal way to obtain threads is blade cutting. It includes:

• cutting external threads with dies ;
• cutting internal threads with taps ;
• turning of external and internal threads with threaded cutters and combs;
• thread milling of external and internal threads with disk and worm mills ;
• cutting external and internal threads with thread-cutting heads;
• restoration of damaged external and internal threads with an ordinary or specialized file ;
• vortex processing of external and internal threads.

Rolling is the most high-performance thread processing method, ensuring the high quality of the resulting thread. Thread rolling includes:

• rolling external threads with two or three rollers with radial, axial or tangential feed;
• rolling of external and internal threads with thread rolling heads ;
• rolling external threads with flat dies;
• rolling external threads with a roller-segment tool;
• rolling (extrusion) of internal threads with chipless taps.

Abrasive machining of threads includes grinding with single-thread and multi-thread circles. It is used to obtain precise, mainly running threads.

Extrusion by pressing is used to obtain threads from plastics and non-ferrous alloys. Not widely used in industry.

Casting (usually under pressure) is used to obtain low-precision threads from plastics and non-ferrous alloys.

Electrophysical and electrochemical processing (for example, electroerosive , electro-hydraulic) is used to obtain threads on parts from materials with high hardness and brittle materials, for example, hard alloys, ceramics, etc.

For a long time it was believed that a threaded connection, along with a wheel and a gear transmission , is a great invention of mankind, which has no analogue in nature. However, in 2011, a group of scientists from the Karlsruhe Institute of Technology published an article in the journal Science on the structure of joints in weevil beetles of the species Trigonopterus oblongus living in New Guinea ^[6] . It turned out that the legs of these beetles are connected to the body by means of a trochanter , which is screwed into the coke (basin) - an analog of the hip joint in insects. On the surface of the swivel there are protrusions resembling a conical screw. In turn, the surface of the coke is also provided with a threaded recess. Such a connection provides a more reliable attachment of the extremities than the hinge, and guarantees the insect leading to the woody lifestyle more stability.

The use of helical surfaces in technology began in ancient times. It is believed that the first screw was invented by the Architect Tarentsky , a philosopher , mathematician and mechanic who lived in the 4th – 5th centuries BC. e. The screw invented by Archimedes is widely known for moving liquids and loose bodies. The first carving fasteners began to be used in ancient Rome at the beginning of our era. However, due to the high cost, they were used only in jewelry, medical instruments and other expensive products.

Running and fastening threads were widely used only in the Middle Ages . The external thread was fabricated as follows: a rope greased with chalk or paint was wound onto a cylindrical billet, then a helical groove was cut along the spiral marking formed. Instead of nuts with internal thread, bushings with two or three pins were used .

In the XV – XVI centuries, the production of three- and four-sided taps for cutting internal threads began. Both mating parts with external and internal threads for screwing were manually adjusted for each other. Any interchangeability of parts was completely absent.

Prerequisites for interchangeability and standardization of threads were created by Henry Maudslay around 1800 , when he invented a screw-cutting lathe that made it possible to cut precision threads. He made the lead screw and nut for his first machine manually. Then he turned a screw and a nut of higher precision on the machine. Replacing the first screw and nut with new, more accurate ones, he machined even more precise parts. This continued until the accuracy of the thread ceased to increase.

Over the next 40 years, interchangeability and standardization of threads took place only within individual companies. In 1841, Joseph Witworth developed a fastener system that, thanks to the adoption of many English railway companies, became the UK national standard, called Whitworth British Standard (BSW). The Whitworth standard served as the basis for the creation of various national standards, for example, Sellers standard in the USA, Löwenherz threads in Germany, etc. The number of national standards was very large. So, in Germany at the end of the 19th century there were 11 carving systems with 274 varieties .

In 1898, the International Congress for the Standardization of Thread in Zurich defined new international standards for metric threads based on Sellers threads, but with metric dimensions.

In the Russian Empire, there was no standardization of threads at the state level. Each enterprise that produced threaded parts used its own standards based on foreign analogues.

The first measures to standardize threads were taken in 1921 by the People's Commissariat of Railways of the RSFSR . Based on German metric carving standards , he issued tables of NKPS-1 norms for carvings used in railway transport. The tables included metric threads with a diameter of 6 to 68 mm.

In 1927, on the basis of these tables, the Committee for Standardization under the Council of Labor and Defense developed one of the first state standards of the USSR - OST 32. In the same year, OST 33A was developed for threads according to Whitworth standard. By the beginning of 1932, OSTs for trapezoidal threads were developed based on modernized American Acme standards .

In 1947, the International Organization for Standardization (ISO) was founded. ISO thread standards are currently generally accepted throughout the world, including Russia.

• Pipe thread
• Worm-gear

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• Ed. Ishlinsky A. Yu. New Polytechnical Dictionary. - M .: Big Russian Encyclopedia, 2003. - S. 671. - ISBN 5-7107-7316-6 .
• Yakukhin V.G., Stavrov V.A. Manufacture of threads. Directory. - M .: Mechanical Engineering, 1989 .-- S. 192.

• Thread Presentation Program
• Calculation of a threaded connection with the design calculation