Determine the pitch of the metric thread. Overview of varieties of threaded connections. How to determine the pitch of a metric thread


Proper use of it allows you to measure linear quantities in various situations, and for a variety of objects, ranging from the tread of the tire, and ending with plastic flexible tubes. How to measure with a vernier caliper — examples and consistency — these are discussed further.

Measurements in the design and manufacture of threaded connections

The bolt-nut connection is one of the most common in mechanics. In the design and manufacture of structures, the task of how to measure a bolt with a caliper is often difficult.

Before work, it is worth remembering that the main dimensions of the bolt / nut are the length of the product and the diameter of the thread. A standard bolt of any design does not require such measurements. Another thing is when the bolt is made in artisanal conditions, or you need to measure the fastener without dismantling the connection. The following situations are possible here:


Measurements of the sizes of the tread pattern

How to measure tire tread if it is necessary to assess the degree of wear? The depth gauge, which measures along the entire generatrix of the tire tread, will help. It should be noted that wear is almost always uneven, and the number of measurements should be at least 3 ... 5, moreover, on sections of the tire tread uniformly accepted for evaluation. Before measurements, the tire should be thoroughly cleaned of dirt, dust and fragments of small stones stuck inside.

Sometimes it is necessary to solve the problem of how to measure the tread of a tire with a caliper to determine the degree of uniformity of wear. This sets the wear of the tread tires not only in depth, but also in the radius of the transition from the circumference of the protrusions to the circumference of the depressions. Do so. The depth of the pattern is measured on a new tire tread, and then the linear size of the visually changed zone on the used part. The difference will determine the degree of wear and help make the right decision to replace the wheel.

All measurements are carried out by a depth gauge, which must be installed strictly perpendicular to the tire tread.

Measurement of tread wear by a columbic

Diameter measurements

How to measure the diameter with a caliper? Distinguish parts with constant and variable cross-sectional length. The latter include, in particular, reinforcing bars. How to measure the diameter of the reinforcement with a caliper? It all depends on the reinforcing profile, which can be:

  • roundabout;
  • sickle;
  • mixed.

The easiest way to measure such parameters of reinforcement in the second case. First, the height of the protrusions of the profile is determined by external measuring jaws, and then by the depth gauge, the size along the depression. Measurements must be made in two mutually perpendicular directions, since the fittings, and even produced not at specialized enterprises, often have an ovality of cross-section. After that, according to the tables of standard reinforcing profiles, the most suitable value is found (special accuracy is not required here). How to measure the diameter of the reinforcement with a caliper if it has a different type of profile? Here, instead of the diameter of the protrusions, the diameter of the protruding part of the crescent notches is determined, and then they proceed in the same way as the previous case.

When measuring the internal dimensions of pipes use the internal measuring scale of the tool. How to measure the thickness of the pipe with a caliper, especially if the clearance is small? It is enough to calculate the difference between the outer and inner diameters and divide the result into two.

Linear dimensions

How to measure linear dimensions with a caliper? It all depends on the material of the part / workpiece. For rigid elements, the product is firmly pressed to some base plate, after which the measurement is performed by the external measuring jaws of the tool. First, you must establish the suitability of the existing type of caliper for work. For example, the main measuring scale on the bar should be longer than the part by less than 25 ... 30 mm (taking into account the intrinsic width of the jaws). When using a depth gauge, this value is even smaller, since the frame length should also be taken into account (for the most common tools 0-150 mm and with an accuracy of 0.05 to 0.1 mm, this parameter is taken at least 50 mm).

How to measure the cross section of a wire with a vernier caliper? Non-metallic products are flexible, and therefore significantly distort the result obtained in the usual way. Therefore, a rigid steel part (screw, nail, piece of bar) should be introduced into the cambric, and then determine the diameter of the wire section with external jaws. Similarly, if you want to know the internal size of the wire.

The question - how to measure the chain with a caliper - is often asked by cyclists, since the wear of the chain, defined as the distance between its adjacent links, allows you to decide on replacing the product. The outer jaws are set to a distance of 119 mm and inserted into the link, after which they are stretched to the sides until a further increase in size is impossible (to facilitate work, the chain can be preloaded with tensile force). Deviation from the original size will show the actual wear, which must then be compared with the maximum allowable.

Operational purpose of the thread

Fixing thread  provides a complete and reliable connection of parts under various loads and at different temperature conditions. This type includes metric.

Mounting and sealing thread  Designed to ensure the tightness and impermeability of threaded joints (excluding shock loads). This type includes metric  fine pitch pipe cylindrical  and conical  thread and conical inch  thread.

Running thread  serves to convert rotational motion into translational. She takes great effort at relatively low speeds. Threads belong to this type: trapezoidal, stubborn, rectangular, round.

Special thread  It has a special purpose and is used in selected specialized industries. These include the following:

- metric tight thread  - thread made on the rod (on the stud) and in the hole (in the socket) for the largest limit sizes; Designed to form threaded connections with interference;

- metric thread with gaps  - a thread with necessary to ensure easy screwing and loosening of threaded joints of parts operating at high temperatures, when conditions are created for the setting (splicing) of oxide films that cover the thread surface;

- hour thread  (metric) - thread used in the watch industry (diameters from 0.25 to 0.9 mm);

- thread for microscopes  - thread, designed to connect the tube to the lens; has two sizes: 1) inch - diameter 4/5 I (20.270 mm) and pitch 0.705 mm (36 threads per 1І); 2) metric - diameter 27 mm, pitch 0.75 mm;

- ocular multi-thread  - recommended for optical instruments; thread profile - isosceles trapezoid with an angle of 60 0.

Figure 104 - Classification of threads

Advantages and disadvantages of threaded connections
  Advantages of threaded connections:
- high load capacity and reliability;
  - interchangeability of threaded parts in connection with the standardization of threads;
  - ease of assembly and disassembly of threaded joints;
  - centralized manufacture of threaded joints;
  - the ability to create large axial compressive forces of parts with a small force applied to the key.

Disadvantages of threaded connections:
  - the main disadvantage of threaded connections is the presence of a large number of stress concentrators on the surfaces of threaded parts, which reduce their fatigue resistance under variable loads.

Axial load distribution over thread turns

The axial load is distributed unevenly over the threads of the nut thread due to an unfavorable combination of screw and nut deformations (the turns in the most extended part of the screw interact with the turns of the most compressed part of the nut).
  The statically indefinable problem of the distribution of the load along the turns of a rectangular thread of a nut with 10 turns was solved by Professor N.E. Zhukovsky in 1902.

The first round transfers about 34% of the total load, the second - about 23%, and the tenth - less than 1%. It follows that it makes no sense to use too high nuts in the fastener. The standard provides for a nut height of 0.8d for normal and 0.5d for low nuts used in lightly loaded joints.

To balance the load in the thread, special nuts are used, which is especially important in joints operating under cyclic loads.

Metric thread

Metric thread  (Fig. 120). The main type of fastening thread in Russia is a metric thread with an angle of a triangular profile a equal to 60 °. The dimensions of its elements are given in millimeters.

This is the main type of fastening thread designed to connect parts directly to each other or using standard products with a metric thread, such as bolts, screws, studs, nuts.

According to GOST 8724-81, metric threads are made with large and small pitch on surfaces with diameters from 1 to 68 mm - over 68 mm, the thread has only a small pitch, and the small thread pitch can be different for the same diameter, and a large thread has only one value. A large step in the symbol of the thread is not indicated. For example: for a thread with a diameter of 10 mm, the large pitch of the thread is 1.5 mm, and the shallow one is 1.25; one; 0.75; 0.5 mm

According to GOST 8724-81, the metric thread for diameters from 1 to 600 mm is divided into two types: with a large pitch (for diameters from 1 to 68 mm) and with a small pitch (for diameters from 1 to 600 mm).

Large pitch threads are used in joints subject to impact loads. Fine-pitch thread - in the joints of parts with thin walls and to obtain a tight connection. In addition, fine threads are widely used in adjusting and setting screws and nuts, since it is easier to make fine adjustments with it.

When designing new machines, only metric threads are used.

The metric thread is marked with the letter M:

M16, M42, M64 - with a large step

M16 × 0.5; M42 × 2; M64 × 3 - with a small step

· M42 × 3 (P1) - this means that the thread is multi-start with a diameter of 42 mm, a pitch of 1 mm and its stroke is 3 mm (three-way)

· M14LH, M40 × 2LH, M42 × 3 (P1) LH - if you need to mark the left thread, then after the symbol mark the letters LH

How to determine the pitch of a metric thread

· 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.

Inch thread

There is currently no standard governing the basic dimensions of an inch thread. The previously existing OST NKTP 1260 was canceled, and the use of inch threads in new designs is not allowed.

This is a carving of a triangular profile with an apex angle of 55 ° (and equal to 55 °). The nominal diameter of the inch thread (outer diameter of the thread on the shaft) is indicated in inches. In Russia, inch threads are allowed only in the manufacture of spare parts for old or imported equipment and are not used in the design of new parts.

As mentioned earlier, the birthplace of a standardized thread can be considered Britain with its English system of measures. The most prominent English engineer-inventor, preoccupied with tidying up threaded parts, is Joseph Whitworth ( Joseph whitworth ), or Joseph Whitworth, is also correct. Whitworth turned out to be a talented and very active engineer; so active and adventurous that the first threaded standard developed by him in 1841 BSW   It was approved for universal use at the state level in 1881. To this point the thread BSW   became the most common inch thread not only in the UK, but also in Europe. The fruitful J. Whitworth has developed a number of other standards for inch threads for special applications; some of them are widely used to this day.

  •   The first number indicates the main diameter of the screw.

    • Abroad, in the USA, thread diameters are measured in inches, lines, dots, and miles. There are diameters from # 0 to # 10, where # 0 is the smallest size (6 points) and # 10 is the largest (1 line, 9 points). Diameters # 12 and # 14 are also found, but are usually used only in old equipment that requires repair and restoration. Number # 14 approaches 1/4 inch in diameter, but not exactly 1/4 inch. Starting with # 1 thread (7 points, 3 miles), the diameter increases by 13 mils, so thread diameter # 2 is 0.086 inches, # 3 is 0.099 inches and so on. For screws greater than # 10, the first number indicates the diameter in inches. So a 1 / 4-20 screw in diameter is a quarter of an inch.
    • If the thread is metric, for example M3.5, the first number after M means the main diameter in millimeters.

  •   The second number shows the distance between two thread elements of the same name.  This number expresses the step, for example, between two turns. Pitch is measured in millimeters, fractions of an inch or the number of threads per inch.

    • In the USA, the number of threads per inch is used. For example, a 1 / 4-20 screw has 20 threads per inch.
    • In the metric system, the pitch between the turns is measured in millimeters. So, for the screw M2 x 0.4, the distance between the turns is 0.4 mm. Although there are more than two pitch standards in the metric system, thread pitch is often not indicated; therefore it would be nice to take a sample with you.
      • The basic metric standards for screws are DIN and JIS. These standards are closely related and identical in places, but the JIS M8 bolt may not fit the DIN M8 bolt. There is also an American ANSI metric standard.

  •   Read the screw length after x.   The length of the screw is measured from the end of the screw to the beginning of the head, as shown in the illustration. Note that the length of countersunk screws is measured with it.

    • The length of American screws is measured in inches. So, a screw length of 1 / 4-20 x 3/4 is three quarters of an inch, or seven and a half lines. The length is expressed either in simple fractions, or decimal.
    • The length of the metric screws is indicated in millimeters.

  • Other marking.

    • The landing class is also applied, the part will spin freely or tightly. Classes 2A or 2B are mainly used. “A” indicates that it is an external thread, and “B” that it is internal, as on nuts. The number "2" indicates the average tightness of twisting, other numbers (1 or 3) are much less common.
    • There are UNC, UNF or UNEF markings. By these standards, the pitch of the thread is different. The most commonly used UNC.
    • Inner diameter. It is equal to the diameter of the hole in the nut blank before threading. In most cases, the outer diameter of the corresponding insertion part is indicated.

    • In the modern world, threaded connections are very common. It is characterized by high reliability and practicality in use. A rather large number of different parameters are distinguished that can be used to determine the parameters of the fastener in question. The most important step can be called. It is indicated on almost every drawing and various technical documentation.

    Thread pitch concept

    Thread is used to connect a wide variety of products. To determine the thread of the bolt, you need to consider the distance between the honey with the same sides of the profile. The features of this concept include the following points:

    1. To determine the main parameters, a measurement is required.
    2. Inaccurate results can be found when applying the ruler.
    3. To increase the accuracy of measurements, it is necessary to analyze several threads. That is why, depending on the length of the threaded surface, an analysis of 10 to 20 turns is carried out.
    4. Measurements in millimeters are recommended. In some cases, the number translates to inches.

    The distance between the troughs can be measured using a special tool. The thread gauge is represented by a combination of special steel plates that have special cutouts. Different values \u200b\u200bare applied on the surface.

    Measurement methods

    There are quite a number of different ways to determine the pitch of a thread. All of them are characterized by their specific features that need to be considered. Common methods include:

    1. Using a regular ruler.
    2. The use of a special tool that can be used to determine the value in question. A thread tester can be purchased at a specialist store.
    3. A caliper is an accurate tool. It is used quite often because of its high accuracy and versatility in use.

    All the above methods provide fairly accurate data. It is easiest to take measurements using a tool that determines the thread, but you can get by with a standard caliper.

    Coil Measurement Process

    When considering how to determine the thread pitch, the features of the selected method should be considered. When using the ruler, it is enough:

    1. Measure the length of the rod on which the profile was applied. It is worth considering that when measuring the entire length of the rod, and not just the part, you can determine a more accurate result.
    2. Count the number of turns.
    3. Carry out a depth measurement to determine the main parameters of the threaded connection.

    In this way, only the average can be determined. If errors were made in the process of cutting the turns, then the distance between them may differ slightly.

    An example of a measurement is as follows:

    1. 20 turns are counted.
    2. We measure the length of the rod, for example, the figure was 127 mm.
    3. We divide 20 turns by the length of the rod, as a result we get an indicator of 6.35 mm. It corresponds to the pitch of the threads in millimeters.

    To convert to inches, it is enough to divide the calculated value in millimeters by 25.4. The result is a result of 0.25 or ¼ inches. With self-measurement, there may be an error, so the result is rounded to an approximate standard value.

    On sale you can also find special patterns that can be used to check the characteristics of the thread. A similar procedure is quite simple to perform:

    1. The most suitable template is selected. On sale you can find just a huge number of special templates, which are represented by a plate with a specific profile. A similar element is not expensive, you can purchase it in various specialized stores.
    2. It is applied to the surface to control key indicators. The template should go in without obstacles, and no space should be formed between the plate with the working surface.

    If the template easily goes into the grooves, then you can determine the basic parameters of the surface.

    In addition, it is possible to take measurements using a caliper. This tool is widespread. Step-by-step actions are as follows:

    1. Depth gauge sets the height of the rod.
    2. The next step is to count the number of turns. It is quite difficult to do this, you can use a marker to indicate already counted profile threads.
    3. The information obtained allows us to calculate the slope.

    It is possible to determine the indicator in question when measuring directly between adjacent peaks. It is recommended to clean the surface. Otherwise, it is almost impossible to get an accurate result.

    Measurement Nuances

    When using a caliper, several recommendations should be considered. An example is the following information:

    1. If there is a plate between the head and the end part of the product, then in this case it is recommended to use the main measuring scale and depth gauge. With a similar process, it is possible to obtain indicators of the thickness of the washer, the height of the head, the thickness of the intermediate element. Such data allow you to calculate the main parameters of the threaded connection.
    2. The accuracy of the results can be significantly improved by cleaning the surface of various pollutants. To do this, you can use abrasive material or special fluids to remove corrosion.

    You can carry out the procedure in question yourself. As a rule, there are no problems.

    In conclusion, we note that manufacturers indicate the step and many other important indicators. As a rule, they are applied to the head or other element.

    A threaded connection is the main way of joining two structural elements together. In plumbing and construction practice, threaded connections are used in the installation of pipelines, valves and fittings and connecting to the engineering systems of consuming equipment.

    This article presents threaded connections. We will consider their varieties, components of the fasteners, methods for determining the size and configuration of the thread.

    Article Content

    Purpose and scope

    The thread, according to the provisions of GOST No. 2.331-68, is defined as a surface formed by a combination of alternating depressions and protrusions of a certain profile, located on the inner or outer walls of the body of revolution.

    The functional purpose of the thread is:

    • keeping parts at the required distance in relation to each other;
    • fixing parts and limiting the possibility of their displacement;
    • ensuring the density of the joints of the joined structures.

    The basis of any thread is a helix, depending on the configuration of which the following types of thread are distinguished:

    • cylindrical - thread formed on a cylindrical surface;
    •   - on the surface of a conical shape;
    • right - thread, the helix of which is directed clockwise;
    • left - with a helix counterclockwise.

    A threaded connection is the joining of two parts by means of a thread, ensuring their immobility or a given spatial movement relative to each other. Such compounds are classified into two main categories:

    • connections obtained using special connecting elements - screws, studs, nuts and washers (this includes all varieties);
    • connections formed by screwing two joined structures without third-party fasteners (in plumbing -).

    The current GOST defines the following basic parameters of the thread:

    • d is the nominal outer diameter of the screw or bolt, indicated in millimeters;
    • d 1 - the inner diameter of the nuts, the size of which must coincide with the value d of the mating fastener;
    • p is the thread pitch indicating the distance between two adjacent ridges of the helix;
    • a - profile angle, indicates the angle between adjacent protrusions of the helical line in the axial plane.

    The thread pitch determines whether it belongs to the main or minor class. In practice, the differences between them are that small threaded connections (in this configuration all fasteners with a diameter of 20 mm are made), due to the minimum distance between the ridges of the helix, are more resistant to self-unscrewing.

    Advantages and disadvantages

    The widespread use of threaded connections is due to the presence of many operational advantages in this fastener method, which include:

    • reliability and durability;
    • the ability to control the compression force;
    • fixation in a predetermined position due to the self-braking effect;
    • the ability to assemble and disassemble using widespread tools;
    • comparative simplicity of design;
    • an extensive assortment and sizes of fasteners, their low cost;
    • minimum dimensions of fasteners in comparison with the dimensions of the connected parts.

    The disadvantages of these connections include uneven load distribution along the helical thread line (about 50% of the pressure falls on the first turn), accelerated wear and weakening of the joint with frequent disassembly of fasteners and its tendency to self-unscrew under the influence of vibrational loads.

    Differences between metric and inch threads (video)

    Varieties of threaded connections

    Depending on the type of profile, the thread is classified into the following varieties:

    • metric;
    • inch;
    • pipe cylindrical;
    • trapezoidal;
    • persistent;
    • round.

    The most common is metric thread (GOST No. 9150-81). Its profile is made in the form of an equilateral triangle at an angle of 60 0 with a pitch of turns from 0.25 to 6 mm. Fasteners are available in diameters of 1-600 mm.

    There is also a metric conical type thread that uses a 1:16 taper. This configuration ensures joint tightness and locking of fasteners without the need for lock nuts. The table below indicates the main parameters of the metric profile.

    Inch thread does not have regulatory standards in domestic construction documentation. The inch profile is made in a triangular shape with an angle of 55 0. The profile step is determined by the number of turns in a 1 ″ long section. The design is standardized for fasteners with an outer diameter from 3/16 ″ to 4 ″ and the number of turns per 1 ″ from 3 to 28.

    The conical inch thread has a profile angle of 60 0 and a taper of 1:16. This profile provides high tightness of the connection without additional sealing materials. This is the main type of thread in hydraulic and pressure pipes of small diameters.

    Pipe thread of cylindrical type (GOST No. 6357-81) is used as a fastening and sealing. Her profile has the shape of an isosceles triangle with an angle of 55 0. In order to obtain increased tightness, the profile is made with rounded upper faces without additional gaps at the places of depressions and protrusions. This type of thread is standardized for diameters of 1/16 ″ -6 ″, the pitch varies between 11-28 turns per 1 ″.

    Pipe thread is always performed in a shallow configuration (with a reduced pitch), which is necessary to maintain the wall thickness of the connected structures. This type of profile is widely used to connect steel pipelines of heating and water supply systems and other cylindrical parts.

    Trapezoidal thread (GOST No. 9481-81) is most often used in screw-nut fasteners. The profile has an equilateral trapezoidal shape with an angle of 30 0 (for fasteners of worm gears - 40 degrees). Used in fasteners with diameters of 10-640 mm.

    In comparison with a rectangular profile, a trapezoidal helix, with identical dimensions, provides greater joint strength. This configuration allows you to effectively perform moving gears (turns rotational motion into translational), which is why trapezoidal threads are widely used in running nuts that fix the rod of the pipeline valves.

    Thrust thread (GOST No. 24737-81) is used in fasteners that experience strong unidirectional axial loads during operation. Its profile is made in the form of a versatile trapezoid, one of the faces of which has an angle of 3 0, the opposite - 30 0. The profile pitch is 2-25 mm; it is used for fasteners with a diameter of 10-600 mm

    The round thread profile (GOST No. 6042-83) is formed by interconnected arcs with an angle between the sides of 30 0. The advantage of this configuration is the increased resistance to operational wear, which is why it is widely used in pipeline valve designs.

    How to determine thread parameters?

    When choosing pipe fittings or flange connecting elements, it becomes necessary to find out the type and dimensions of the profile, which is necessary for the correct determination of the parameters of the reciprocal fasteners. In most cases, you will come across a metric thread, which is most common in domestic construction and plumbing.

    The metric profile has a unified designation of the type M8x1.5, in which:

    • M is the metric standard;
    • 8 - nominal diameter;
    • 5 - profile step.

    There are three ways to determine the pitch of a profile — use a special tool (metric thread gauge), compare the pitch of the fixture with the profile, or measure it with a caliper. The determination by the latter method is the simplest - it is only necessary to measure the distance between ten turns of the profile and divide the resulting length by 10.

    The nominal diameter is measured with a caliper along the outer edge of the profile. The table below lists the correspondence of the most common diameters and steps of a metric thread profile.

    When working with inch threads, you can determine the pitch of its profile by attaching an inch ruler to the fasteners and visually counting the number of turns per 1 inch (25.4 mm). Using a special thread gauge, note that the English and American standards differ in profile angle (60 and 55 0, respectively), so here you will need attention when choosing a tool.

    Important: do not forget that the step for metric thread is the distance between adjacent turns of the profile, and for inch - the number of turns per 1 inch.
    

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