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Types of threads used in engineering

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

The thread types on the fasteners are divided into:

  • Internal - are applied to nuts, sleeves of anchors, couplings, pipes;
  • External - are located on screws, screws, screws, bolts, stiletto heels.

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

  • Metric - profile in the form of an equilateral triangle (it happens with small, medium and large steps);
  • Inch - triangular or trapezoidal shape;
  • Metric conical - has a triangular profile;
  • Round - the protrusion of the top of the round form;
  • Trapezoidal - protuberance of apex of trapezoidal form;
  • Stubborn - trapezoidal asymmetric profile;
  • Modular - trapezoid shaped profile;
  • Tubular conical and cylindrical (profile has the form of an isosceles triangle of an inch size with a rounded (or flattened) apex and a coil crest);
  • Conical inch - profile with a cut-off vertex of triangular shape.

There are still such types of threads as square and rectangular. They are applied to fastening elements by screw-cutting lathes according to individual drawings. Such types of threads do not allow obtaining high-precision accuracy, so they are rarely used. There are no GOSTs on them.

To date, for general machine-building applications, the main external and internal thread is metric. In the drawings, it is indicated by a large letter "M" indicating the outer diameter in millimeters. Tube types of threads are used to connect various pipes. Their nominal diameter is the internal diameter of the pipes outside of which the thread is cut. In the drawings, it is indicated by the 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 directory of the machine builder. For metric threads reference data are described in detail in accordance with GOST 9150-81, 24705-81 and 8724-81. For tube cylindrical threads, dimensions are given in GOST 6357-81.

One of the common fasteners with metric thread is a bolt. It is a metal rod with a head at the end. The length of the rod is marked with a helical groove. The purpose of bolts - the connection of various parts of mechanisms and structures with a nut. The head of the bolt is hexagonal and shaped (secret, semicircular, butt, mortgage, terminal).

There are the following types of bolts for the purpose:

  • Furniture - used to join products in furniture production;
  • Machine-building - are used in the industry of industrial importance;
  • Lemeshnye - designed for the coupling of machinery in the agricultural sector;
  • Road - are used to connect various metal structures and road barriers.

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