Two Commonly Used Bolts: Description of Carriage Bolts And Hexagon Bolts

In the fields of mechanical manufacturing, construction, and daily equipment installation, bolts are indispensable fasteners, with a wide variety of types. Among them, carriage bolts and hexagon socket head bolts, with their unique structures and properties, play important roles in their respective fields.

Carriage bolts, also known as round head square neck bolts, get their name from being widely used in carriages initially, and their structural design is quite ingenious. Their heads are round with smooth surfaces, without cross or slotted grooves, and there is a square neck connected under the head. This square neck is the "highlight" of the carriage bolt. When it is installed on a workpiece with a square hole, the square neck can perfectly fit into the prefabricated square hole of the connected part, effectively preventing the bolt from rotating during the tightening process and greatly simplifying the installation process. The screw part of the carriage bolt is engraved with threads, which can be full threads or partial threads, depending on the actual connection requirements.

In terms of material selection, carriage bolts are quite diverse. Common ones include ordinary carbon steel, which has low cost and is suitable for some scenarios with low requirements on strength and corrosion resistance; stainless steel has good corrosion resistance and is often used in humid environments with corrosive media, such as outdoor wood structure connections and water treatment equipment; there are also some high-strength alloy carriage bolts that can be used in mechanical structures bearing large loads.

Carriage bolts have a wide range of application scenarios. In wooden structure buildings, they can firmly connect wood, and the round head will not easily hook clothes or scratch the human body like other bolts; in the simple connection of steel structures, they are easy to operate and can quickly fix components; they can also be seen in some large machinery such as agricultural machinery and mining equipment, used to fix some non-critical parts.

Hexagon socket head bolts have completely different appearances and characteristics from carriage bolts. Their heads are cylindrical, with a hexagon socket groove on the top of the head, which is where their name comes from. This hexagon socket design requires the use of a special hexagon socket wrench for installation and disassembly. Compared with ordinary hexagon head bolts, their head size is smaller, which can adapt to some installation environments with limited space.

The thread precision of hexagon socket head bolts is relatively high, which ensures the tightness and stability during the connection process. Their materials are also abundant. In addition to common carbon steel and stainless steel, there are also high-strength alloy steels. After heat treatment, they have extremely high strength and hardness, can bear huge loads, and are suitable for occasions with high requirements on connection strength, such as the connection of key components in precision machinery, mold manufacturing, and automobile engines.

In terms of installation, due to the large contact area between the hexagon socket groove and the wrench, hexagon socket head bolts can transmit greater torque when tightened, making the connection more firm. However, during installation, it should be noted to avoid using wrenches with mismatched sizes to prevent damage to the hexagon socket groove, which may lead to failure in normal disassembly or tightening.

The application of hexagon socket head bolts is mainly concentrated in fields that require connection precision and space. In precision mold manufacturing, they can accurately connect various parts of the mold together, ensuring the precision and service life of the mold; in electronic equipment, due to their small heads, they do not take up too much space and can meet the needs of miniaturization and precision of electronic equipment; in automobile manufacturing, a large number of hexagon socket head bolts are used in some key engine components and chassis components to ensure the reliability of the connection.

In terms of installation precautions, each has its own focus. When installing carriage bolts, it is necessary to ensure that the size of the square hole on the connected part matches the square neck of the bolt. If the square hole is too large, the anti-rotation effect will be lost; if the square hole is too small, it may cause the bolt to be unable to be installed or damage the workpiece. When tightening, the force should be moderate. Excessive tightening may cause the bolt to break or damage the connected part.

For hexagon socket head bolts, before installation, check whether the hexagon socket groove is damaged and whether the wrench matches the bolt specification. During the tightening process, apply force evenly to avoid bolt  due to uneven force, which may affect the connection effect. At the same time, in some occasions with large vibrations, it is necessary to regularly check the tightness of the hexagon socket head bolts to prevent loosening.

From the perspective of market application, carriage bolts, due to their simple structure and low price, have a large demand in some civil and industrial fields with low connection requirements; while hexagon socket head bolts, due to their high precision and high strength, are increasingly used in high-end manufacturing, precision machinery and other fields, and the market has increasingly high requirements for their quality and performance.