Overview and classification of bolts

Overview and classification of bolts

A bolt is a threaded fastener with a cylindrical rod at the head. A cylindrical part with a thread on one end is called a double head bolt, used to fit with a nut. The other end is called the bolt head, which is called the bolt head. Bolts are usually made of metal. Bolts used in special occasions, such as electrical insulation or anti-corrosion materials, also have various non-metallic materials.

Bolts are used for connecting or fastening in mechanical structures or building components, and are usually classified as fasteners in mechanical components. In most cases, bolts are manufactured according to relevant national or international standards. Therefore, during operation and cycling, bolts are also classified as standard parts along with other parts produced according to mandatory standards. Bolts, screws, and nuts (also known as nuts) are commonly referred to as screws or non professional descriptions in many fields.

The difference between bolts and screws lies in two aspects: firstly, the shape, which strictly requires that the double head bolt part of the bolt be cylindrical for installing nuts, but sometimes the double head bolt part of the bolt is conical or even central. Another is the use of functionality, where the object of the screw is the target material rather than the nut. In many cases, bolts can work independently and can be screwed into pre drilled holes without the need for nut and bolt coordination. At this point, bolts are classified as screws based on their functionality. There are many types of bolts, but most of them are different from bolts and bolt heads.

1. Cylindrical threads can be divided into coarse threads, fine threads, and inch threads, hence they are called fine thread bolts and inch bolts;

2. The shape and purpose of bolt heads are different, including hexagonal head bolts, square head bolts, half round head bolts, countersunk head bolts, perforated bolts, T-head bolts, hook heads (anchor bolts), etc.

3. The bolts are derived from expansion bolts and other related parts.

Based on the material and manufacturing accuracy of the bolts, high-strength bolts, high-precision bolts, and locking bolts can be obtained.

5. Bolts are divided into more than ten grades based on their performance levels, including 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, and 12.9.

Bolts of grade 8.8 and above are made of low-carbon alloy steel or medium carbon steel and undergo heat treatment (quenching and tempering), commonly referred to as steel structural bolts, while the rest are commonly referred to as ordinary bolts. The bolt performance level marking consists of two parts of numbers, representing the nominal tensile strength value and yield strength ratio of the bolt material, respectively

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