The through-hole nut fastener is also called the standard part in the market. It is the general name of a kind of mechanical parts used when fastening two or more parts (or components) into a whole. It is characterized by a wide variety of specifications, different performance and uses, and a high degree of standardization, serialization and generalization. Fasteners are the most widely used mechanical basic parts, which are in great demand.

Fasteners are a kind of mechanical parts which are widely used for fastening connections. A variety of fasteners can be seen on various machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments, instruments and supplies. It is characterized by a wide variety of specifications, different performance and uses, and a high degree of standardization, serialization and generalization. Therefore, some people call a class of fasteners in the existing national standards as standard fasteners, or abbreviated as standard fasteners. Fasteners are the most widely used mechanical foundations. With China's accession to the WTO in 2001, China has entered the ranks of major international trade countries. Fastener products of our country are exported to many countries in the world. Fastener products of all countries in the world are also pouring into the Chinese market. Fasteners, as one of the products with large import and export volume in China, are of great practical and strategic significance to promote Chinese firms to enter the world and to promote their full participation in international cooperation and competition. Due to the specifications, dimensions, tolerances, weights, properties, surface conditions, marking methods of each specific fastener product, as well as the specific requirements of acceptance inspection, marking and packaging projects.

Twill nut

Common Testing Instruments

The most important link in the development and design of fasteners is the quality control. There are several major ports from feeding to finished product delivery, which have different inspection methods. First of all, feeding is related to appearance, size, elements, performance, harmful substances detection, etc. In the process, more is appearance, size, knock test, forging streamline; heat treatment is more appearance, hardness, torque, tension, metallography, etc. Surface treatment is more hydrogen embrittlement test, coating, salt spray, etc. Including that the shipment has a harmful substance detection. In size and appearance detection, the common ones are quadratic element, profilometer, coordinate measuring instrument, image sorter (this is a complete sorter); in mechanics and chemistry detection, there are mainly hardness machine (Lowe and Vickers), tension machine, metallographic microscope; in material detection, there is a spectrum analyzer, salt spray test machine.

With China's accession to the WTO in 2001, China has entered the ranks of major international trade countries. Fastener products of our country are exported to many countries in the world. Fastener products of all countries in the world are also pouring into the Chinese market. Fasteners, as one of the products with large import and export volume in China, are of great practical and strategic significance to promote Chinese firms to enter the world and to promote their full participation in international cooperation and competition. As the specifications, dimensions, tolerances, weights, properties, surface conditions, marking methods of each specific fastener product, as well as the specific requirements of acceptance inspection, marking and packaging, are stipulated in several national (industry) standards, such as British, German and American standards.

It usually includes the following 12 types of parts:

Bolt: A type of fastener consisting of a head and a screw (a cylinder with external threads). It needs to be matched with a nut to fasten and connect two parts with through holes. This connection form is called bolt connection. If the nut is screwed off from the bolt, the two parts can be separated, so the bolt connection belongs to the removable connection.

Screw: No head, only one kind of fastener with threads at both ends. When connecting, one end must be screwed into a part with an internal thread hole, the other end must pass through the part with a through hole, and then the nut is screwed up, even if the two parts are tightly connected into a whole. This form of connection is called stud connection and also belongs to removable connection. It is mainly used in situations where one of the connected parts is thicker, requires compact structure, or is not suitable for bolted connection because of frequent disassembly.

Screw: It is also a kind of fastener consisting of head and screw. It can be divided into three categories according to its use: machine screw, fastening screw and special purpose screw. Machine screw is mainly used for a part with fixed threaded holes, and a part with through holes between the fastening connection, do not need nut coordination (this connection form is called screw connection, also belongs to the removable connection; can also be matched with nuts, for two parts with through holes between the fastening connection). Fixing screw is mainly used to fix the relative position between two parts. Special purpose screw such as ring screw for lifting parts.

Nut: With internal threaded holes, the shape is generally flat hexagonal cylinder, but also flat square cylinder or flat cylindrical, with bolts, studs or machine screw, used to fasten the connection of two parts, so as to make it a whole.

5. Self-tapping screw: similar to machine screw, but the thread on the screw is special thread for self-tapping screw. It is used to fasten and connect two thin metal components to form a whole. Small holes need to be made in advance. Because of its high hardness, the screw can be directly screwed into the holes of the components to form a response internal thread in the components.

6. Wood screw: It is similar to machine screw, but the thread on the screw is a special wood screw thread, which can be directly screwed into the wooden component (or part) for fastening a metal (or non-metal) part with a through hole to a wooden component. The connection is also removable.

7. Gasket: A kind of fastener with flat circular shape. Placing between the support surface of bolts, bolts or nuts and the surface of connecting parts plays a role in increasing the contact surface area of connecting parts, reducing unit area pressure and protecting the surface of connecting parts from being damaged. Another kind of elastic washer can also play a role in preventing the loosening of nuts.