How are bolts measured? Examples of measurements with a caliper. Measurements in the design and manufacture of threaded connections

Without fasteners, a master is like without hands: dealing with a fixed connection of parts various designs has to constantly. Bolts, screws, nuts, screws, washers - the most common fasteners. In work, it is very often important to know the size of the bolt in advance.

You will need

Calipers;
- ruler.

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Instruction

Bolts and nuts, similar to modern ones, appeared around the middle of the 15th century. They were made exclusively by hand, and therefore each nut-bolt combination was unique. The classic version of the connection of these two parts has been improved over the years.

Among the latest industrial achievements is the development of special electronic devices, capable of automatically controlling the tightening forces of this type of fastener.

A modern bolt is a popular fastener. Together with a nut, it is intended for detachable connection of parts and is a cylindrical rod with external thread on one end and a head on the other. The head can be of different shapes: square, oval, cylindrical, conical, six or four faces. Most of the state standards for fasteners, including bolts, provide for the possibility of producing similar products (according to general view, by appointment). The difference will be only in the type of bolts and their execution. The size of the bolt depends on the purpose and is primarily related to the outer diameter of the thread, since the bolt is a threaded fastener. To determine the diameter of a bolt, measure it outside diameter threaded with a caliper. If the thread is not applied along the entire length of the rod, then the diameter of the bolt in its “bald” part is approximately the same as the diameter of the thread when measured at the tops of the turns. What is the length of the bolt? As a rule, when designating a product, the length of its rod is indicated. Thus, the height of the head is not taken into account. Measure the length of the rod - get the length of the bolt. If you order a M14x140 bolt in metric measurement, this means you need a bolt with a thread diameter of 14 mm, a shank length of 140 mm. In this case, the total overall length of the product, taking into account the height of the bolt head, for example, 8 mm will be 148 mm. Another parameter is the thread pitch of the bolt. Measure the distance between two nearby (neighboring) thread vertices and you will get the desired size. For example, an M14x1.5 bolt is a bolt with a diameter of 14 mm and a thread pitch of 1.5 mm. Another dimensional characteristic of some types of bolts is the length of the threaded end. To find out, measure the part of the rod that is intended for screwing the nut. There are many regulations that technical requirements to the fixture. For example, for flange connections (and it is with them that bolts are used), they are set out in GOST 20700-75. Both the design and dimensions of fasteners are regulated by GOSTs 9064-75,9065-75, 9066-75. How simple

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Even a person who is far from technology often has to unscrew and tighten screws, bolts, nuts (hardware - this is often abbreviated as these hardware) with a tool designed for this - wrenches. Each key is marked with the size of its working part, simply - the pharynx. But the value corresponding to it - turnkey size - denoted in technical reference books by the letter S (the distance between opposite parallel faces on a nut, bolt or screw head), is not indicated on any fastener. As a rule, these data are not available in the operating and repair instructions attached to any technique, even in the symbols and drawings, although there is plenty of other information about fasteners in them: both the thread size and its pitch are indicated, sometimes the length and even view heat treatment, often the tightening torque. But basically these data are constructive, and they are needed for the manufacture of parts. During adjustment, repair or assembly work, the above thread parameters, except for the latter, turn out to be unclaimed. For a mechanic, it is much more important to know with what size of the throat a wrench is needed for the head of one or another screw or bolt and nut (or, as the professionals say, “wrench for how much”).

When the nut or bolt head is in plain sight and in an easily accessible place, it will not be difficult to determine “how much” a key is needed - an experienced techie will recognize this at a glance, and an inexperienced one can “calculate” with a caliper or by selecting keys: from two -Three times this is usually done successfully.

If the fastener is in hard to reach place, and even “behind the eyes” (which happens very often), then it is necessary to determine the size of the turnkey hardware head by touch, when even a professional can easily make a mistake. Trouble will not happen if the master tries to work with a smaller key - he simply will not fit on the head. If the key turns out to be large, then “cutting off” the edges of the head with it, as they say, is a couple of trifles. In addition to the fact that the part will be irreparably damaged, then unscrewing the fasteners even with a special tool will be a considerable problem.

To determine the “turnkey” size “behind the eyes”, it makes sense to refer to the information on the thread of the fastener specified in the instructions. After all, according to GOST, each thread corresponds to two close sizes of the turnkey fastener head: the main and the reduced one, and the difference in their values ​​is small. On average, the turnkey size is approximately 1.5 times the outer diameter of the thread (see Table 1) and you can already focus on it. And although the reduced turnkey size is assigned by designers less often than the main one, it is necessary to try to unscrew the fasteners “behind the eyes” for the above reasons with a smaller key: if it doesn’t fit, then you can safely work with a key corresponding to the main size - it will not break (of course, provided that the fasteners are not rusted). The keys are usually also made according to the same principle: at one end of the pharynx (open - for open-end, closed - for socket and ring keys) corresponds to the main size of the head of the fastener, at the other - reduced. Only combined keys fall out of this row, in which at both ends the pharynx is of the same size, only one is open, and the other is closed (circular), and wrenches are adjustable.

Matching the dimensions of a turnkey fastener to its nominal metric thread diameter

When working with fasteners for their safety, the tool has essential, therefore, only serviceable keys should be used: their pharynx should not be expanded, and the sponges should not be wrinkled. Keys with such defects must be removed from the working set. In addition, seemingly similar tools differ significantly in the quality of the metal, the profile of the jaws. The last condition directly affects the distribution of forces on the edges and edges of hardware.

Fasteners are designed for a specific tightening torque when assembling the product. However, often the efforts during disassembly, especially those that are “boiled” or rusted threaded connections exceed it many times. In these cases, it is better to use the appropriate socket or ring (professionals call them ring) wrenches, and not open-end wrenches. Moreover, you cannot use an adjustable wrench, as well as when unscrewing small (less than S10) nuts, bolts and screws.

Combined pipe wrench.

If the edges of the fastener are severely damaged by corrosion or for some reason turned out to be “rolled up”, in order to still unscrew it, it is necessary to grind off the turnkey edges by a “number” less. Then, having impregnated the threaded connection with a special liquid (or, in extreme cases, kerosene) to soften the rust and after waiting for time, try to unscrew the part again. Another way (but not the last) to unscrew a bolt or screw with a damaged head is to make a slot between opposite faces for a strong screwdriver and try to unscrew the fastener with this tool. And finally - use a pipe wrench for this. By the way, in the nomenclature of the latter there are now those that do not damage the edges and edges of fasteners even at high unscrewing torques. For small nuts, special pliers can be used.

When you have to deal with the adjustment and repair of the same equipment (for example, a personal car) on a regular basis, it will be useful to compile a table of turnkey sizes for fasteners of the main adjustable units, devoting special time to this or as you turn to adjusting one or another mechanism or unit.

Regular key heads:

Key heads with dynamic profiles:

a - end; b - cap.

Forces on faces and edges of threaded fasteners from socket (a) and ring (b) wrenches with different internal profiles:

I - concentrated; II - distributed.

Table 2 shows the turnkey dimensions of the main and adjusting threaded connections for the VAZ-2105 car.

Some fasteners and their turnkey dimensions in VAZ vehicles

Since we are talking about cars, it is worth noting that the so-called “balloon” “for 19” and “candle” “for 21” keys are on a special account in the tool kit of the Zhiguli (and other cars).

The first one is made quite peculiarly and stands out from the whole set of keys. It is recognized even by those who are little familiar with technology: it is cap-shaped, with a curved lever handle, the end of which is made in the form of a screwdriver sting. Once upon a time, with the help of this key, chrome wheel covers were removed, which are no longer installed on modern cars. It would be advisable to sharpen it a little and thus have a strong screwdriver in the kit. In addition to loosening and tightening wheel bolts, this wrench can also be used when working with other relevant fasteners. If necessary, the wheel bolts can also be unscrewed with a conventional (box and even open-end) wrench "19".

The second - a "candle" wrench in appearance is similar to similar tubular socket wrenches with the same diametrical hole for the knob. It even retains a ratio of 1.5 of the diameter of the turn-off thread (14 mm) to the distance between the opposite faces of the key (21 mm). If we turn again to Table 2, it will become clear that the key is non-standard, and there is no special and other key with the same size in the kit. The thread on the candle, although standard (14x1.25), is one of the non-recommended ones.

And about one more key - the usual carob "for 10". This wrench, like a fire extinguisher, is always better to keep "at hand" - as they unscrew the nuts of the battery terminals. After all, if necessary, for example, in case of a short circuit in an electrical circuit or (which has also become relevant now) to turn off an alarm that has worked for no reason (if it does not “obey” the key fob), this must be done very quickly.

It should be noted that in the automotive tool kit there are keys for far from all sizes of fasteners. Therefore, when you need to crawl under a car (in a pit or overpass), it will not be superfluous to check whether everything necessary tools taken with them, otherwise you will have to crawl out from under it with nothing. The same must be done if you are going to disassemble some assembly or assembly for repair or maintenance. In addition, very often some kind of universal and even special devices. Without all this, disassembly may be impossible or even in vain.

One remarkable moment: fasteners with a turnkey size of “13” appeared in our country along with the Zhiguli car, the prototype of which, as you know, was the Italian FIAT-124. With their appearance, hardware with turnkey sizes “by 12” and “by 14” has lost its position.