M12 M20 Carbon steel Round head Philip crosses tapping metal screws grade8.8 Black coating

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. Self-cutting tapping screws have the following types: cross recessed pan head self-cutting tapping screws, cross recessed countersunk head self-cutting tapping screws. Cross recessed raised countersunk head self-cutting tapping screws, hexagonal head self-cutting tapping screws.
3. Self-extruding tapping screws (self-tapping lock screws) - Self-extruding tapping screws thread is generally machine thread, rarely use self-tapping thread. In the wrenching method, in order to ensure the use of high-speed automatic assembly wrenches, generally do not recommend the use of slotted. Self-extruding self-tapping screws have a three-pronged screw cross-section. So also known as triangular thread screws.
4. Self-drilling tapping screws (self-drilling screws) - Self-drilling tapping screws thread, China, Germany and international standards for self-tapping thread. U.S. ASME and SAE standards in the BSD type self-drilling tapping screws for self-tapping thread, CSD type self-drilling tapping screws for machine thread. Self-drilling tapping screws do not recommend the use of 'slotted' and 'ordinary hexagon head'.
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. Only the U.S. standard metal drive screws, our country and the German standard is not.
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, the surface of more phosphate treatment (phosphating).
7. Fibreboard nails - Cross slot for Z-type, the surface treatment is mostly plating. Fibreboard nails have the following types of several types: countersunk head, double countersunk head fibreboard nails, pan head, pan head flange (with pad) fibreboard nails, half countersunk head, half countersunk head flange (with pad) fibreboard nails.
8. Combination of self-tapping screws - Ordinary self-tapping screws, self-cutting self-tapping screws, self drilling self-tapping screws and flat washers, elastic washers (including spring washers, elastic lock washers shaped t into a combination of self-tapping screws.
9. Other self-tapping screws type - High and low teeth double lead self-tapping screws, coarse and fine teeth (different pitch) thread self-tapping screws, thread coated with sealing material (drop-resistant) self-tapping screws, a variety of composite groove self-tapping screws, other special equipment juice self-tapping screws.

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 or high-speed planetary 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.
 
The meaning of the bolt performance level is an international common standard, the same performance level of the bolt, regardless of the difference between its material and origin, its performance is the same, the design of only the performance level can be selected.
Strength grade so-called 8.8 and 10.9 grade refers to the bolt's anti-shear stress level of 8.8GPa and 10.9GPa.
8.8 Nominal tensile strength 800N/MM2 Nominal yield strength 640N/MM2
General bolts are used "X.Y" to indicate the strength, X * 100 = the tensile strength of the bolt, X * 100 * (Y/10) = the yield strength of the bolt (because according to the logo: yield strength / tensile strength = Y/10)
Such as 4.8 grade, the tensile strength of the bolt is: 400MPa; yield strength is: 400 * 8/10 = 320MPa.

Blackening treatment has the following advantages:

• Improved rust prevention - The protective film of iron tetraoxide (black rust) on the surface of parts is in a strong and stable state.
• Less likely to flake off - Blackening is a surface treatment process that merely changes the surface of the part into a different substance by triggering a chemical reaction, which is difficult to peel off.