Share the basic knowledge of fasteners?

Fasteners are a type of mechanical parts that are used for fastening and connection and are widely used. It is widely used in various industries, and can be seen in various machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments, chemicals, meters and supplies, etc. It is the most commonly used mechanical basic part. It is characterized by diverse varieties and specifications, different performances and uses, so the degree of standardization, serialization, and generalization is also low. Therefore, some people call a type of fasteners that have national standards as standard fasteners, or simply standard parts.
The parameters that need to be marked to describe the fasteners are: product name (standard), specification, material, strength grade, and surface treatment. Such as: DIN912, M4-0.7x8, SCM435, 12.9 grade, blackened.

1. Product name (standard): Note: For screws without standard, they are non-standard parts, and drawings are also required.

For example, DIN912, the Chinese name is: hexagon socket head screw, which is the product name.

But the most accurate way is to call the standard, because GB70 is also the same name; but the two standards have many dimensions and are never the same.

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

2. Specification, usually the name of the screw is the diameter of the tooth pattern * the length of the screw.

The nominal diameter of the tooth pattern, the common ones in the metric system are: M2, M3, M4, M5, M6, M8, M10, M12, etc.;

Common ones in American system are: 4#-40, 6#-32, 8#-32, 10#-24, 1/4-20, 5/16-18, 3/8-16, 1/2-13, etc.

Therefore, the screw length refers to the exact length of the embedded object. For example, the total length of the countersunk head screw is loaded, and half the length of the half head is added to the half countersunk head screw, so the length of the cylinder head screw never includes the head size. Such as:

For specifications, the full name should be plus the pitch. For example, M4-0.7x8, the outer diameter of the 4 fingers is 4mm, 0.7 means the distance between the two crests is 0.7mm, and 8 means the exact length of the embedded object is 8mm.

In order to simplify, never write the tooth pitch, we default the coarse tooth to the standard tooth, because it is the most common; this way, it will never be marked. This is the case for the metric system, and American products still have to be marked with tooth pitch.

Here is a pilot to talk about the specifications of American screws, such as 6#-32*3/8, 6# is the outer diameter of the tooth, which is close to 3.5mm; 32 is 32 threads per inch of thread length (equivalent to the thread of a metric screw). Distance); 3/8 is also the length of the screw (exactly the same as a metric screw).

Here are two formulas to remember: tooth outer diameter A#=(Ax0.013+0.06)x25.4(mm), 1 inch=25.4mm.

Among them, 2#=2.2mm, 4#=2.9mm, 6#=3.5mm, 8#4.2mm, 10#=4.8mm are data to be memorized. The number of teeth corresponding to the screws of each specification should also be memorized: 2#-56, 4#-40, 6#-32, 8#-32, 10#-24, 1/4-20, 5/16-18 , 3/8-16, 1/2-13 (American standard teeth).

Note: American UNC teeth are standard teeth, and UNF is fine teeth. We will default coarse teeth to standard teeth.