Black M16 M20 Carbon steel Flat head Hexagon tapping screws Class8. 8 CSK screws

Product Description:

1. Ordinary self-tapping screws: The thread is 'self-tapping thread', also known as 'wide thread'. The surface is mostly plated.
2. Self-cutting tapping screws: China's standard called 'self-tapping screws shaved end', the thread for the self-tapping thread or machine thread, cross groove is also 'H' type.
3. Self-extruding tapping screws (self-tapping lock screws): Thread is generally machine thread, rarely use self-tapping thread.
4. Self-drilling tapping screws (self-drilling screws): Self-drilling tapping screws thread, China, Germany and international standards for self-tapping thread.
5. Metal drive screws (metal tapping screws): Metal drive screws thread for the multi-head, and with a certain helix angle of the special thread.
6. Wallboard tapping screws (drywall nails): Wallboard white tapping screws for the trumpet head, cross groove (H-type), 60° tooth angle of the special thread.
7. Fibreboard nails: Cross slot for Z-type, the surface treatment is mostly plating.
8. Combination of self-tapping screws: Ordinary self-tapping screws combined with washers.
9. Other self-tapping screws type: Including high and low teeth double lead self-tapping screws, coarse and fine teeth thread self-tapping screws, etc.

Although there are many types of self-tapping screws, they all have the following common points:

• They are generally manufactured from carburised steel (99% of total production). They can also be manufactured from stainless steel or non-ferrous metals.
• The product must be heat-treated. Carbon steel self-tapping screws must be carburised, and stainless steel self-tapping screws must be solution-hardened.
• High surface hardness, good core toughness. That is, 'soft outside'. This is a major feature of the performance requirements of self-tapping screws.
• The surface of the product requires surface protection treatment, generally plating treatment.
• Cold heading process is adopted. Recommended high-speed cold heading machine and high-speed thread rolling machine production.

Class 8.8 bolts have higher strength than class 4.8 bolts. The number 8.8 represents its material strength grade, which provides greater tensile strength and torque tolerance than Class 4.8 bolts.

Class 8.8 bolts are usually used for some occasions that require large loads or important connections, such as the assembly of Bridges and large mechanical equipment. Class 8.8 bolts have high reliability and durability, which can ensure the fastness and safety of the connection.

Grade 4.6 bolts, which means:

The nominal tensile strength of the bolt material is 400 MPa grade;
The yield strength ratio of the bolt material is 0.6;
The nominal yield strength of the bolt material reaches 400 x 0.6 = 240 MPa level.
Performance grade 10.9 high-strength bolts, the material of which is heat-treated to achieve:
The nominal tensile strength of the bolt material reaches 1000MPa grade;
The yield strength ratio of the bolt material is 0.9;
The nominal yield strength of the bolt material reaches 1000×0.9=900MPa grade.

In practical applications, appropriate grades of bolts should be selected according to specific engineering requirements and design requirements:

• If the engineering structure does not have high strength requirements for bolts and the budget is limited, you can choose 4.8 class bolts.
• For connections that need to withstand strong or heavy loads, class 8.8 bolts should be selected to ensure the safety and reliability of the connection.

Blackening treatment has the following advantages:

• Improved rust prevention: The protective film of iron tetraoxide on the surface inhibits the formation of red rust.
• Less likely to flake off: Unlike plating, blackening is a surface treatment process that merely changes the surface of the part into a different substance.