Previously, furniture was assembled using wooden dowels and corners. Now there are more convenient and durable fasteners. Furniture bolts are widely used along with confirmations and eccentric ties. They are somewhat different from conventional building bolts with hex head, they provide reliable fastening of furniture parts and do not spoil its appearance. Of course, when you buy a ready-made table or bed, few people are interested in the type of fasteners used, but if you decide to assemble furniture at home or repair a factory product, you will have to figure out how to choose the right furniture bolts, what types and sizes they are, what materials and what standards are made.
# 1. Distinctive features of furniture bolts
The bolt is one of the most common fasteners. Everyone knows that it consists of a head and a cylindrical rod. There is a thread on the rod, onto which the nut is screwed. The most common construction bolts have a hexagonal head and are used both in private construction and in the construction of industrial facilities. There are also particularly durable machine-building and road bolts, countersunk plow bolts (used in agriculture), as well as rarer rail and elevator bolts.
The furniture bolt even looks different from the usual construction bolt. First of all, it is “betrayed” by a semicircular hat. The rod can be fully or partially threaded. There is a mustache or square head under the head. This element is necessary so that when the nut is tightened, the bolt does not turn, and the fastener does not loosen. The headrest or mustache rests against the wooden piece of furniture and prevents unnecessary rotation.
The semicircular head, due to the absence of sharp edges and any protrusions, ensures maximum safety in the operation of furniture with such fasteners. It is impossible to catch on the furniture bolt, it does not spoil the appearance of the product, since after installation only the smooth surface of the head will rise above the part. These bolts are found in every modern chair, sofa and bed.
For production, they mainly use galvanized stainless steel. Hard plastic and aluminum bolts are less common. In terms of strength, furniture bolts are inferior, for example, to machine-building ones, but they also cost several times cheaper. Yes, there is no such heavy load on furniture fasteners, but this does not mean that you can buy the first bolts that come across. It is better to check with the seller for a certificate of conformity and quality – this is a guarantee that the fasteners made will be reliable and durable. High-quality and certified products are sold by the Rusmetiz store: furniture bolts presented on the page https://rus-metiz.com/categories/bolty, are sold in different sizes, and if you have any difficulties with the choice, experts will always give expert advice.
# 2. Scope of application of furniture bolts
Where else can furniture bolts be used than in the furniture industry? Everything is correct. The main purpose of this fastener is to connect furniture parts, but the convenient design with a semicircular head was highly appreciated by builders and began to be used in other areas.
At the moment, furniture bolts are used for the following purposes:
- in the production of tables, chairs, sofas, beds, wardrobes, chests of drawers, kitchen sets and other furniture;
- when repairing furniture when old bolts need to be replaced. By the way, when you move, furniture can be disassembled by unscrewing some of the fasteners, and assembled at a new place using existing bolts, because they are not disposable;
- for joining wooden parts in private construction and repair, for example, when creating stairs and gazebos;
- in some other areas (mechanical engineering, road works, construction of bridges, production of door locks), when it is necessary that the height of the head is minimal, and the site itself is not responsible.
No. 3. Manufacturing standards and size of furniture bolts
A quality furniture bolt is one that is produced in full compliance with the standard. It remains to figure out what kind of standards are used, because there are several of them:
GOST 7801-81 is devoted to bolts with a mustache and an enlarged semicircular head. According to it, bolts with a thread with a cross section of 6 to 20 mm are produced (in the marking M6-M20). Head height ranges from 3 mm for M6 to 10 mm for M20, head section – from 14 to 44 mm, respectively. Bolt length can be from 25 to 200 mm, thread length – from 18 to 46 mm, whisker height – from 3 to 9 mm. Some bolt lengths are not available in this standard. Weight of 1000 pieces of the smallest bolts (M6, length 25 mm) – 6.5 kg, and the largest (M20, length 200 mm) – 484.3 kg;
GOST 7802-81 regulates the geometry of square head bolts. The thread section of such bolts is from 5 to 24 mm (M5-M24), and the head section is from 11 to 52 mm. Depending on the size, the head height is 2.5-12 mm, the headrest is from 3 to 15 mm, the size of the head on each side is from 5 to 24 mm. Thread length from 16 to 60 mm, length of all fasteners – 12-260 mm. The weight of the smallest bolts is 2.7 kg / 1000 pieces, the largest is 911 kg / 1000 pieces.
DIN 603 is a German standard, an analogue of our GOST 7802-81, but in some respects it differs slightly from it. The standard allows the production of M6-M8 bolts from hard plastics; for M10-M20 bolts, it is imperative to use stainless steel (A4 or A2), as well as brass compositions. The bolts of the standard receive a head with a diameter of 12.45-46.8 mm and a height of 2.7-11.05 mm. The height of the head is 2.9-14.1 mm, the length of the thread is 16-65 mm, the length of the fasteners is 16-200 mm, the head protrudes 4.52-20.84 mm on each side. The mass of 1000 pieces of products is from 4 to 597 kg.
It is better to look for the exact dimensions that this or that fastener should have in the official standards and focus on these indicators when buying. The nuts are selected according to the size of the bolt.
Do not confuse furniture bolts with furniture screws. The latter receive a hexagonal head, which is completely recessed into the product during installation. The screws are produced according to DIN 912 and our standard 11738.
No. 4. Furniture bolt material
We have already touched on this topic indirectly, considering various standards, but now we will consider in more detail. Previously, furniture bolts were made of metal that was not protected from corrosion. Even if the humidity level in the operating room is normal and the rivers do not flow, the mount all the same began to rust over time. It’s all the fault of natural moisture. Not only does this hardware gradually lose its strength, but if it is necessary to disassemble some piece of furniture and remove the nut from the bolt, difficulties arise – it firmly “clings” to the thread, and it is almost impossible to remove it, and even in a hard-to-reach place. This problem has long been eliminated – today’s bolts do not corrode, as they are made from the following materials:
stainless steel with a galvanized coating of white or yellow, bolts with an additional chrome coating are less common;
brass and copper bolts are less common and more expensive;
The vast majority of furniture bolts are made of galvanized stainless steel. In the marking, the manufacturer must indicate the grade of steel used:
- A2 (domestic analogue – 08X18H10) is an excellent material that does not corrode, almost does not magnetise, withstands temperatures from -200 to + 4250C;
- steel A4 (10X17H13M2) contains 2-3% molybdenum, due to which it is even more resistant to moisture and acids, therefore, fasteners made of such material are used even in aggressive environments. Bolts of accuracy class A come out of steel of class A2 and A4 (more on this below);
- other types of steels are also used in production, for example, 38XA, 30HGSA, 10KP, 20KP, 10KP, 20G2R, 10, 35 and others. Information on steel grades and strength is collected in the table.
No. 5. Strength class
The grade of steel and the features of its processing determines the strength class of the finished product. According to regulatory documents, 11 strength classes are determined, here are some of them: 3.6, 4.6, 5.6,…, 10.9, 12.9. It is not difficult to decipher these numbers:
- the number to the comma (dot) indicates the ultimate tensile strength, N / mm2. We get the exact value if we multiply the number by 100. For a bolt of strength class 4.6 it will be 4 * 100 = 400 N / mm2;
- the number after the decimal point is the ratio of the yield point to tensile strength, expressed as a percentage. For the same bolt 4.6, this parameter will be 60%. The yield point is considered to be such a load that causes irreversible deformations of the product.
In the furniture industry, bolts are used from class 4.6 to 12.9. The most popular are hardware of classes 4.6, 5.6, 5.8, 6.6 and 6.8. However, if critical parts are to be fastened, then bolts 8.8 must be used. They are called high strength. In general, all fasteners that can withstand 800 N / mm2 or more are called high-strength. Furniture bolts of even higher strength are much less common on the market and are more expensive.
Bolts of low strength are made, as a rule, by turning. For more durable products, forging is used, and the most durable ones are also hardened.
No. 6. Accuracy class
The standards define three accuracy classes: A, B and C. Each class has its own manufacturing tolerances, each class differs in thread roughness, the difference in the diameter of the rod and the bearing surface of the head.
- Bolts of class C are used when making connections that do not require calculations. It is the most popular type of bolt in the furniture industry. Such fasteners are installed in a hole that is 2-3 mm larger than the diameter of the rod. If you apply some effort to the parts connected in this way, then you can notice small movements caused by the difference in diameter.
- Class B bolts are placed in holes 1-1.5 mm larger than the diameter of the rod, therefore, a more serious approach is required when calculating and creating holes;
- Bolts of class A are made with the most accurate geometry and are installed in holes created exactly for their diameter (only 0.25-0.3 mm larger). This type of fastener is created only by turning, which ensures both high strength and excellent accuracy. There is only one minus – the cost.
No. 7. What else to consider when buying?
It is probably unnecessary to explain that the durability and reliability of the manufactured furniture will depend on the quality of the bolts. No one wants to be on the floor in the middle of the night because the bed was assembled with bad bolts. And you won’t wish anyone to fall from a chair or stairs. It is impossible to be 100% sure of the reliability of the future fastening, but it is possible to estimate some parameters of the bolt, which will indicate its quality:
- fasteners that do not corrode are made by galvanizing. If you twist such a hardware in your hands and scratch the coating a little, no traces will remain on your hands. If the manufacturer cheated and covered the product with silver paint (for galvanizing), then traces of the coating will remain on the hands;
- find a nut of the correct size and try to screw it onto the bolt. If the process went through without any difficulties, then the manufacturer produced a quality product with good geometry;
- choose only reliable and reputable stores that will not risk their reputation. Ask for certificates of conformity for the goods – a normal manufacturer will have all the documents.
Finally, we note that if you are not entirely sure that you can independently choose suitable furniture bolts, then it makes sense to use the help of a professional, and in the future you yourself will be able to distinguish high-quality hardware from low-quality ones.