Metric thread: dimensions. Metric thread: GOST

It is well known that threaded is one of the most common detachable joints that allow to perform assembly and disassembly works without damage to the integrity of structures, machines and mechanisms. The basis of this connection is the thread applied on two or more surfaces of the bodies of rotation, which is basically divided according to the indicators described below. The classification of threads is presented in the table below.

Thread metric

Screw cutting on or in the material, which has a profile of the tooth in the form of an isosceles triangle, is a metric thread, its dimensions are measured in millimeters. According to the shape of the application surface, this thread is cylindrical, but can be conical.

The latter is most popular in use, especially for the following fasteners:

• Bolts;
• Anchors;
• Screws;
• Hardware;
• Hairpins;
• Nuts and stuff.

Screw cutting, applied to the base of the conical shape, is called a metric taper thread. It is used in places requiring fast locking of joints, without additional sealing and with the termination of leakage by simple pulling along the axis. Used for the installation of plugs and pipe connections:

• Oil;
• Oil;
• Gas;
• Water;
• Air.

It is important to know that the tapered and cylindrical threads have the same profile, which makes it possible to screw them together. Metric threads are classified by size, direction of rotation, step and additional parameters that are reflected in the marking.

Metric thread dimensions

The spread of diameters of this thread in the industry has a range from 0.25 to 600 mm, with a diameter of more than 68 mm the thread is only shallow, whereas up to this value it varies. Thread with a large pitch is used in joints under large and shock loads. It is also interesting that at a large thread the pitch is always fixed in relation to the diameter, in contrast to the small one, which can vary, which is separately and additionally indicated in the marking.

For example, if "M16" is encountered in technical documents or drawings in the joints of parts, this means that the letter M means metric thread. The dimensions of the outer diameter of the turns are 16 mm, and the large step of the standard thread is 2 mm, according to the information given in the table (the thread of the second row is indicated in parentheses). So, the thread is metric: the main dimensions (GOST 24705-2004).

Fine-pitch threads

In the marking, a small step is indicated after the diameter. It looks like this: "M16 × 0.5", where, as already known, M is a metric thread. The dimensions of the outer diameter are 16 mm, with a step size of 0.5 mm. Interestingly, after a diameter of 2 mm, the difference between the thread pitch becomes noticeably noticeable, leading to separation. And products of equal diameter have several types of steps of fine carving, like those considered in 16 mm:

• 1.5 mm;
• 1.0 mm;
• 0,75 mm;
• 0.5 mm.

As an example, a part of the table is given, which makes it possible to understand and clearly evaluate the range of fine threads, without taking into account the large step considered earlier.

Metric thread: basic dimensions (GOST 24705-2004)

Specified parameters

In multi-thread threads, the step is indicated separately (in parentheses), and in its place the number of visits is indicated. Here's how this and other additional parameters are indicated when labeling:

• (P1) - where P is a step of 1 mm, and turns - 3 (example: M42 × 3 (P1));
• LH - left thread (example: M40 × 2LH);
• MK - metric thread tapered (example: MK24x1.5);
• EG-M or GM, Where G denotes the thread on the cylindrical base of the wire insert or fitting (example: EPL 6-GM5);
• G, h, H is the tolerances field, is the tolerance of the mean diameter in combination with the protrusion diameter (example: M12-6g), and for different internal and external diameters, both tolerances are denoted in the marking (example: M12-6g / 8H).

Thread diameters

There are indicators specified in the summary tables, which are important to consider in cases where the metric thread is considered - the dimensions Diameters:

• External (D and d);
• Internal (D _{1 and} d ₁ );
• Average (D _{2 and} d ₂ );
• Internal on the bottom of the cavity (d ₃ ).

When widely used in the threaded joint of the sliding fit, the average diameter has become more important, and in cases of equality of the values, the largest D ₂ bolts and the smallest D ₂ nuts.

Large letters D denote the values of the diameters of internal threads, and the parts applied to the outer surface are denoted by small letters - d. The numbers indicate the location. The degree of accuracy of the tolerance fields is classified by letter symbols: E, F, G, H, d, e, f, g, h, and, as in diameters, the letter indicates the location.

Ratio of metric and inch threads

In contrast to European countries and countries close to them, where the metric system became widespread after the reign of Napoleon, in the countries of the former colonies of Britain and its satellites all measurements take place in the imperial system. In this system, the measurement of the threads and their connections is made in inches.

Screw cutting, which has a profile of the tooth in the form of an isosceles triangle, with a peak angle of 55 degrees. (In the UTS standard for the USA and Canada - 60 degrees) is called an inch thread, its dimensions are in inches, and the pitch is in the number of turns per inch (1 "= 24.5 mm) .Such fixing threads are made in the range From 3/16 ", the designation indicates only the outer diameter.

Dimensions of inch and metric thread Measured with a caliper, and if in the case of a metric thread this will be enough, then in the inch after measurement use a special table. When measuring threads, special templates are used, but there is also a popular way of measuring the step: if you wrap a sheet of paper with a thread, scroll the product several times, a trace is printed on the paper, allowing you to measure the ruler. When using a sheet of paper as a sheet, the need for a ruler is no longer necessary - it is enough to count the number of marks in 2 cells (1 cm) and divide by 10.

Hole dimensions

Getting the threads is due to:

• Cold rolling of rollers and heads;
• Cutting cutters, combs or cutters;
• Cutting dies or taps;
• Accurate casting;
• Abrasive or EDM.

For cutting external threads, the workpiece is cylindrical and chamfered, and under the internal one drill a bit smaller than the required thread metric (size) hole, but larger than its internal diameter. After determining the size of the holes under the metric thread, it must be taken into account that when cutting the notch inside, a partial extrusion of the material subsequently participating in the formation of the threaded profile occurs. It is also important to consider the properties of the material in which the drilling is performed, reducing the drill size by 0.1 mm.

Dimensions of nuts with metric thread

The nut is one of the components of the fastening elements, which has an internal thread. They vary in height relative to diameter and strength, according to purpose and configuration. The most widely used are nuts for key or hex, here is their list with the indication of GOSTs:

• GOST 5915-70 - medium size;
• GOST 15523-70 - high;
• GOST 22354-77 - increased strength;
• GOST 5916-70 - low nut with a recess;
• GOST 10605-94 - for thread diameter more than 48 mm.

There are many nuts and special purpose, here are some examples and their GOSTs:

• Cap type (hexagonal) - GOST 11860-85;
• For manual screwing (nut-lamb) - GOST 3032-74;
• Slotted crown - GOST 5919-73;
• Rounded with a slot - GOST 11871-88, GOST 10657-80;
• Round, with end, radial holes - GOST 6393-73;
• For rigging works (eye-bolts) - GOST 22355 (DIN580, DIN 582).

The most important parameter of threaded connections is the matching of nuts and threads. The values of more demanded threads with a large pitch are indicated in the table below, where S is the key size, e is the width of the nut, and m is its height.

Table of conformity of threads and nuts (GOST 5915-70 and GOST 10605-94)

Standards

The basic thread sizes comply with GOST 24705-2004, which modifies the standard - ISO 724: 1993 (international classification). This GOST since July 1, 2005 is the state standard of the Russian Federation and takes into account the interests of the economy of another 12 countries, formerly members of the USSR, who voted for it. Under its action, metric thread sizes of GOST 9150 for a wide range of purposes are included, as well as diameters and steps of GOST 8724.

By the standards of interchangeability, this GOST refers to the following international and national standards:

• GOST 8724-2002 (ISO 261-1998);
• GOST 9150-2002 (ISO 68-1: 1998);
• GOST 11708-82;
• GOST 16093-2004 (ISO 965-1: 1998 and ISO 965-3: 1998).

This GOST fixes all the main dimensions, possible tolerances, terminology and formulas for calculating diameters:

• D ₂ = D - 2 x 3/8 H = D - 0.6495 P;
• D ₂ = D - 2 x 3/8 H = d - 0.6495 P;
• D ₁ = D - 2 x 5/8 H = D - 1.0825 P;
• D ₁ = D - 2 x 5/8 H = d - 1.0825 P;
• D ₃ = d-2 17/24 H = d = 1.2277 P.

It is difficult to imagine modern life without machines and mechanisms, it is even more difficult to imagine a technique without detachable joints that provides threading. Efficiency, relative ease of manufacture and comfortable use have ensured that threaded connections are an honorable place in world history.