All about high-strength bolts

Know all about high-strength bolts need not only to employees of machine-building enterprises. This information is needed and the most common people who are trying to create complex structures. Differences in species and labels, features of operation, dimensions and mass are extremely relevant.


On high-strength bolts there are official valid GOST 52644-2006. This act is normalized:

  • Bolt dimensions;

  • The length of the thread of such fasteners;

  • variations of structural elements and versions;

  • twisting coefficients;

  • Theoretical mass of each product.

They also apply to the standard DIN 6914. By default, this product has a hexagon turnkey head. It is intended for high-folded steel connections. The fastener diameter can be from M12 to M36. Their size ranges from 3 to 24 cm.

Such bolts can be used in mechanical engineering, in engine. They will also be useful for sites where strong vibration is valid; They can finally use in building structures of various kinds. A big role, however, plays the correctly chosen tightening force. Too weak pressure often leads to premature destruction of the compound, too strong – can harm fastening or connected structures.

The designation in the drawings of high-strength bolts is performed using a triangle symbol, at the top of which (but not in the top!) The vertical and horizontal line intersect.

Areas of use

Some areas of use especially durable fasteners are already named. But it can be used not only for metal structures in construction and mechanical engineering, as often think. These products are also needed for agricultural machinery and for railway mounts. The main feature is the suitability for such mounting compounds that are exposed to a very large load, and where therefore, the standard methods of fixation cannot be applied. Such fasteners are in demand even in the most “heavy” construction – when building bridges, tunnels, high towers and tags.

Any parts of high-strength bolts, of course, must have increased reliability and mechanical fortress. All compounds where such fasteners are used are related to a shifting category. When using such fasteners, it is not necessary to worry or clean the holes. Mink high-strength bolt can not only be in metal, but also to reinforced concrete. Separately, it is worth saying about the bolts under the hexagon.

Outdoor hexagon cuts can have either a standard envelope, or targeted under the small size.

There are still products with a reduced height of the head (and one of their subspecies is designed for small keys). However, the internal hexagon products are good thanks to:

  • more convenience;

  • increased strength;

  • Optimal reliability.

Types and labeling

The strength class of bolts in Russia must correspond to the official GOST. It is customary to allocate 11 categories of such fasteners. The high strength group includes only products not lower than class 9.8. The first digit when multiplying 100 gives the indicator of the greatest strength. Multiplication on 10 second digits allows you to establish a correlated maximum strength.

The high-strength bolt should be designed to operate in a harsh climate if it is marked with the letters “HL”. The designation “U” says that the product will withstand the average degree of cooling. Controlled tension connections must be entered into a special magazine. The estimated value of the twisting force cannot be exceeded by more than 15%.

Returning to the marking according to GOST 22353-77, it is worth noting such a structure:

  • First, the manufacturer’s alphabetic designation;

  • short-term resistance (in megapascals), reduced 10 times;

  • Climatic performance;

  • Room performed smelting.

As for GOST 2006, the corresponding marking indicates:

  • branded stigma;

  • Strength category on the current standard;

  • climatic category;

  • Melting number;

  • Letter S (characteristic of products with increased turnkey dimensions).


High-strength bolts are obtained on the basis of carbon steel with the addition of alloying components. Only those steel grades are chosen, which are especially strong and racks for mechanical influences. Exhaust Modern Technologies is a hot or cold “landing of blanks”. Such techniques make it possible to significantly increase the fortress of the alloy produced.

Additionally, heat treatment is carried out in an electric furnace, which guarantees elevated anti-corrosion characteristics and long-term safety of the product; It also boosts the fortress of the product.

Sizes and weight

Learn these parameters is the easiest way to table below:



Gaspark turns


0.111 kg

24 mm


0.118 kg

24 mm


0.282 kg

34 mm


0.198 kg

30 mm

At M24 bolts, key indicators are:

  • Height height 15 mm;

  • envelope turnkey – 36 mm;

  • thread gaps – 2 or 3 mm;

  • Length – at least 60 and no more than 150 mm.

M27 the same parameters will be:

  • 17 mm;

  • 41 mm;

  • 2 or 3 mm;

  • 80-200 mm respectively.



Experts in the 1970s noticed that even high-strength fasteners demand attentive observation in the first 1-3 years. At this time, the “shooting” is likely, even without visible manifestations of external loads. Before use, therefore, very careful cooking is necessary. Hardware reuncture throughout the procedure and purified from dirt, rust. Advanced the threads on the discarded bolts and nuts, after which the lubricant layer is updated.

Preparation is carried out in two different ways. One option implies the use of a lattice capacity (and with small sizes of work, it is simply used a bucket in which the holes are pierced by nail). In the barrel they boil water, where it is desirable to add an arbitrarily selected cleaner. Even powder for manual washing.

When the boiling point is achieved, the container is immersed and kept so from 10 minutes to ¼ hour.

Drain of water, high-strength bolts will need to be loaded for 60-120 seconds to the reservoir, where 85% of gasoline and 15% of the autolant. With preheated metal products, the hydrocarbon will soon disappear, and special oil with a homogeneous layer will be distributed over the surface. As a result, the tightening coefficient will be equal to 0.18. If the spinning coefficient must be reduced to 0.12, paraffinations will be required. Cleaning in this case is performed in a standard way. The next step is the room of nuts for 10-15 minutes in liquid paraffin; After their extraction, it is required to allow excess reagent to drain.


If it is planned to install a bolted fastening with the possibility of further disassembly, it is recommended to compile a special project in which the project load takes into account. Previously, all the designs are inspecting and find out how much they correspond to the instructions of the project and section SNIP III-18-75. Holes combine, and then all parts are connected using mounting plugs. Next will need:

  • in free (not closed) channels to introduce fasteners;

  • evaluate linear parameters of manufactured assemblies;

  • tightly pull the bag;

  • pull the bolts accurately on an effort prescribed in the project;

  • pull out the plugs;

  • Introduce the remaining fasteners in the released passages;

  • stretch them to the required effort.

Fluctuations of the thickness of the elements tested using the probe and the lining can be a maximum of 0.05 cm. If this drop is greater than 0.05 cm, but not more than 0.3 cm, then smooth bending is achieved by smoothing with sandpaper. The procedure is performed on the section up to 3 cm from the Detail Circulation line. The slope should not be cooler 1 to 10.

When calculating the length of the used bolts, primarily the thickness of the package. When the holes are drilled on the treated surfaces, only cooling fluids without oil content can be applied to the bolts. Important: Where high-strength bolts should be used, other types of fasteners cannot be used, even at the assembly stage. This devalues ​​all efforts to improve clutch strength. The fixation of each bolt is made using two washers of the high fortress: one – under the bolted head, and the other is laid under the nut.

Nuts need to tighten with the power recorded in the project. Any other fixation is not needed. At that moment, when the bolt is put, these nuts must unlimited to spin on the cut when exposed to hand. If this condition is not respected, the problem fasteners are replaced, and recognized by substantial products need to repetitive preparatory procedures.

Tensioning the bolts is recommended, accurately adjusting the actual conditions and correspondingly changing the effort.

The calculation of the desired parameter is carried out according to the formula M = PXDXK. These multipliers denote the tensioning force (in kilogram-forces), the nominal diameter, twisting the coefficient. The last indicator is taken at the level of either 0.18 (for bolts according to GOST 22353-77 and 22356-77), or 0.12 (when applying other norms). Spinning coefficients specified in branded certificates cannot be used for calculations. If no more than 15 bolts account for some node, as well as when working in hard-to-reach places, the tension level can be determined using dynamometer keys.

The twisting moment created by the key is registered when the tension is going on. This work should be performed smoothly and without the slightest jerks. IMPORTANT: All dynamometric keys are subject to numbering and taring. The last procedure is carried out before the start of each shift. The actual moment of spinning can not exceed the calculated indicator by more than 20%.

Controllers check all high-strength bolts regardless of the tension method. They should figure out whether all the fasteners are equipped with laid marking. Also controls the stage of the washers under each head, under each nut. The density of the screed in the package is estimated by a probe with a thickness of exact 0.3 mm. This dipstick must meet the barrier in the zone limited to the puck.

All points of the connection should be covered by the artist’s brand and stigmat.

When the bolted fasteners are prepared by parafining, about these stamps the same core is applied the letter “P”. With a minor scale of work, adjust the tensioning force is needed by a manual device for bolts with a cross section of from 20 to 24 mm. The thickness of the package can be up to 14 cm. To the serviced package can be up to 7 working bodies.

The bolt pulling procedure is as follows:

  • Tighten all the fasteners using the installation key with a handle to 0.3 m;

  • Nuts and discover parts cover risks using paint or chalk;

  • Nuts scroll through an angle from 150 to 210 degrees (any key is already suitable);

  • Control tensioning just at the time of twist.

How to unscrew the high-strength bolt, look in the following video.

Rate the article
( No ratings yet )
Add comments

;-) :| :x :twisted: :smile: :shock: :sad: :roll: :razz: :oops: :o :mrgreen: :lol: :idea: :grin: :evil: :cry: :cool: :arrow: :???: :?: :!: