Fasteners are a kind of mechanical parts used for fastening connection and widely used. It is widely used in various industries, such as machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments, chemicals, instruments and supplies. It is the most widely used mechanical infrastructure.

  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 refer to a kind of fasteners in the existing national standards as standard fasteners, or referred to as standard fasteners for short.

  Specifications and Functions of Basic Knowledge of Fasteners

  Basic knowledge of fastener products (specification)

  1. The parameters that need to be marked for describing fasteners are: name (standard), specification, material quality, strength grade and surface treatment. For example: DIN912, M4-0.7x8, SCM435, 12.9 grade, blackening.

  Name (Standard): Note: For screw without standard, which belongs to non-standard parts, drawings should be provided.

  For example, DIN912, the Chinese name is: hexagonal cylindrical head screw, which is the name of the product.

  But the most accurate way is to use the standard of address, because GB70 is the same name, but there are many different sizes between the two standards.

  The most influential standards in the world are German Standard (DIN), International Standard (ISO), Chinese National Standard (GB), American Standard (ANSI) and Japanese Standard (JIS).

  2. Specification, general screw address is thread address diameter * screw length.

  Dental designation diameter, metric system commonly used are: M2, M3, M4, M5, M6, M8, M10, M12, etc.

  The common American products are: 4-40, 6-32, 8-32, 10-24, 1/4-20, 5/16-18, 3/8-16, 1/2-13, etc.

  The screw length refers to the effective length of the embedded object. For example, the countersunk head screw is loaded with the total length, the semi-countersunk head screw should add half the length of the head, while the cylindrical head screw length does not include the head size. Such as:

  For specifications, the full name is best with spacing. For example, the outer diameter of M4-0.7x8, 4 fingers is 4mm, 0.7 means the distance between two teeth peaks is 0.7mm, and the effective length of 8 fingers embedded in the loaded object is 8mm.

  Basic Knowledge of Fastener Products (Functional Chapter)

  I. Functional aspects:

  1. Screw torsion requirements: the external hexagonal screw bears relatively greater torsion, the internal hexagonal screw bears less torsion, the cross slot of the torsion is smaller (so this kind of screw is generally ordinary grade screw).

  2. Assembling outer hexagonal bolts is usually assembled with flexible wrenches, plum blossom wrenches and open wrenches. Flexible wrench assembly efficiency is low, but versatility is strong, suitable for various head specifications of external hexagonal screw; plum wrench efficiency is the highest, but some occasions do not apply, a plum wrench only two heads, it can only be used in two specifications of the head of the external hexagonal screw; open wrench is similar to plum wrench, but it can lengthen the sleeve. Cylinder use. The smaller the specification of the outer hexagonal bolt, the higher the requirement of the edge angle of the outer hexagonal bolt. Otherwise, the head of the outer hexagonal bolt is easy to slip when it is subjected to (wrench) force. In order to save materials, Wenzhou people invented the outer hexagonal cave. Hexagonal screw outside the cave is light in weight, thin in head thickness, easy to slip under force, and the head may be screwed off.

  3. The inner hexagonal screw is assembled with the inner hexagonal wrench. The requirement for the inner hexagonal hole is very high. A larger spanner slips and a smaller spanner cannot be inserted. The smaller the inner hexagonal specifications, the higher the requirements for holes. For some large inner hexagonal screw, as long as there is a qualified opposite side, it can be assembled normally with a wrench; for some small inner hexagonal screw, such as M2 inner hexagonal tightening, the wrench will slip if inserted with a little effort, so a slightly larger opposite side is not qualified. Therefore, the inner hexagonal screw of M2, M2.5 and M3 (especially the tightening products) is easy to slip in the assembly process.

  4. Cross groove screw is assembled with screwdriver, so it does not need too much force, so the strength is only 4.8 grade, occasionally some need high strength screw, as long as carburizing heat treatment.