Hexagonal bolts are currently widely used in the fastener industry. Compared with straight and cross-shaped heads, their assembly is less prone to slipping and the torque is higher. Compared with the dodecagonal and multi-toothed heads, the structure is simple and the cost is low. Therefore, the comprehensive price of hexagonal bolts is relatively high, and it is currently the most used type of bolts on automobiles.
Hexagonal bolts can be divided into inner hexagonal bolts and outer hexagonal bolts. What are the differences between these two bolts? How to choose when applying?
This article introduces the structure, cost, tightening tools, advantages and disadvantages and application range.
Structurally, hexagon socket bolts and external hexagon bolts are easy to distinguish. There is basically no difference in the threaded part. The outer hexagon is that the side of the head is hexagonal, and the head has no depression. In order to increase the pressure bearing area of the head, it can also be made into hexagon flange bolts, which is also widely used.
The outer edge of the head of the hexagon socket bolt is round, and the middle is a concave hexagon. The more common one is the cylindrical head hexagon, and there are pan head hexagon, countersunk head hexagon, flat head hexagon, headless screw, Stop screws, machine screws, etc. are called headless hexagon sockets.
Of course, hexagon socket bolts can also be made into hexagon socket flange bolts in order to increase the contact area of the head.
In order to control the friction coefficient of the bolt head or improve the anti-loosening performance, it can also be made into an outer hexagon combination bolt and an inner hexagon combination bolt.
cost
The threads of the inner hexagon bolt and the outer hexagon bolt are generally formed by rolling, and the thread rolling boards used are basically the same, and there is no obvious difference in cost.
The difference is the manufacturing process of the head, because the structure of the head is completely different, different molds and processes are required, the manufacturing cost of the head of the inner hexagon bolt is higher than that of the head of the outer hexagon thread, the screw master understands, The cost of the outer hexagon bolt is only half of that of the inner hexagon bolt.
tightening tool
It can be divided into assembly in life and production.
Assembling in daily life, the shape of the wrench used for hexagon socket head bolts is "L" shape, one side is long and the other side is short, and the short side is screwed, holding the long side can save effort and tighten the screws better. The outer hexagonal bolt is a wrench with an equilateral hexagonal head, such as adjustable wrench, ring wrench, open-end wrench, etc. As shown in the picture below, veterans have done daily assembly or maintenance at home, and should be familiar with the following two tools.
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The assembly in production, in order to ensure the tightening quality and automation requirements, will be assembled by fixed value torque wrench and high-precision tightening gun, so it needs to match the corresponding tightening sleeve. The sleeve of the outer hexagonal bolt is a concave hexagon, and the inner The socket of the hexagonal bolt is a convex hexagonal shape, as shown in the figure below, there will be a series of matching sockets according to the size of the bolt head.
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Advantages and disadvantages
4.1 Advantages
External hexagonal bolts/screws: good self-locking property; large pre-tightening contact area and large pre-tightening force; wider range of full-thread lengths; reaming holes can exist, which can fix the position of parts and withstand shear caused by lateral forces; The inner part is thinner than the inner hexagon, and the inner hexagon cannot be replaced in some places.
Hexagon socket bolts/screws: easy to fasten; not easy to disassemble; not easy to slip angle; small space; bear large load; can be countersunk, can sink into the interior of the workpiece, more delicate and beautiful, and will not hinder other parts.
4.2 Disadvantages
Hexagon bolts/screws: take up a lot of space and are not suitable for more delicate occasions; they cannot be used for countersunk heads.
Hexagon socket bolt/screw: small contact area and small pre-tightening force; there is no full thread beyond a certain length; the fastening tool is not easy to match, it is easy to slip when twisting, and it is inconvenient to replace; it is difficult to disassemble with a professional wrench when disassembling .
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Application range
It is the advantages and disadvantages of outer hexagonal bolts and inner hexagonal bolts, so how to choose when applying?
If the axial force required for the tightening point is large, that is, the tightening torque is relatively large, and the external tightening space is sufficient, use hexagonal bolts for tightening. If the tightening position has space restrictions, or there is a need to make a countersunk head beautifully, and the axial force required for the tightening point is not large, that is, the tightening torque is not large, then it can be made into an inner hexagon.
Taking a car as an example, where the subframe and the body are connected, several bolts pass through the subframe through the bottom and are tightened to the body, because the bottom is an invisible area, there is no aesthetic requirement, there is no interference in tightening, and the shaft required for tightening The force and torque are relatively large (the bolt is tightened over yield), and it is suitable to tighten the external hexagon bolt for this connection position.
The connection of the interior parts is the visible area of the customer. Usually there are aesthetic requirements, and a countersunk head structure is required. The top of the bolt head needs to be kept on the same plane as the structure of the connected parts, or a layer of covering parts needs to be added on the outside. , the tightening axial force and torque at such positions are also smaller. Therefore, it is very suitable for tightening with hexagon socket head cap bolts or screws.
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If you old irons are still not clear how to choose, then it depends on whether the connection position has the requirements of exquisiteness, beauty, and assembly space restrictions. If so, then choose hexagon socket head bolts/screws. If not, choose hexagonal bolts/screws. After all, hexagonal bolts are cheaper and other requirements can basically be met. This is why the outer hexagon bolts/screws are more widely used than the inner hexagon bolts/screws.
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Experience and conclusion
Hexagon head bolts/screws are currently widely used in various industries because of their simple structure, convenient use, moderate price, and not easy to fail when tightened. Common hexagon head bolts/screws have two structures: outer hexagon and inner hexagon.
In terms of structure, the head structure of the two can be clearly distinguished; the cost of the outer hexagon is half of the price of the inner hexagon bolt; whether in life or production, the tightening tools are different; according to the advantages and disadvantages of the two, the application , If the connection position has the requirements of exquisiteness, beauty, and limited assembly space, then choose the inner hexagon head bolt/screw, if there is no such requirement, choose the outer hexagon head bolt/screw.
