Since The Attack Nails

Self-tapping Screws
Self-tapping screw is a kind of threaded fastener, which drills the female thread in the pre-drilled hole of metal or nonmetal materials.

Product Introduction
Because it is self-forming or can tap the thread that matches it, it has high anti-loosening ability and can be assembled and disassembled. Self-tapping nail materials can be divided into carbon steel and stainless steel, among which carbon steel is mainly 1022 medium carbon steel, which is usually used on doors, windows and iron sheets. Its head is a bearing surface formed by a part whose one end is made into an enlarged shape.
For thread forming and thread cutting, Flat Countersunk head, Oval Countersunk head, Pan head, Hex and Hex washer Head are the most important, which account for almost 90% of all self-drilling screws. The other five types are Flat Undercut, Flat Trim, Oval Undercut, Oval Trim, and Fillister, which are relatively less common.

Development
At that time, it was mainly used for the joint of iron sheets on ducts of air conditioning systems, so it was also called iron sheet screws. After more than 80 years of development, it can be divided into four periods-thread forming, thread cutting, thread rolling and self-drilling.
Thread-forming self-tapping screw is directly developed from tin screw, and for thread forming screws, a hole must be drilled in advance, then the screw is screwed into the hole.
The thread cutting self-tapping screw cuts one or more notches at the tail end of the thread, so that when the screw is screwed into the pre-drilled hole, the tail and the tooth of the screw can be used to cut the matching female thread in a way similar to tapping. It can be used in thick plates, hard or fragile materials which are not easy to be molded.
Threaded self-tapping screws have specially designed threads and tail ends, so that the screws can be rolled into female threads by themselves under intermittent pressure. At the same time, the material around the hole can more easily fill the space of the thread and the tooth bottom of the self-tapping screws. Because its friction force is smaller than that of threaded self-tapping screws, it can be used in thicker materials, the torque required for rotation is better controlled, and the strength after combination is higher. The engineering standard definition of thread rolling self-tapping screw is higher and clearer than that of forming or cutting self-tapping screw in material heat treatment, which makes thread rolling self-tapping screw a real "structural" fastener.
The self-drilling screw does not need pre-drilling, which can save the cost and integrate drilling, tapping and screwing. The surface hardness and core hardness of the drill tail screw are a little higher than those of the general self-tapping screw, because the drill tail screw has an additional drilling operation, and the drill tail screw still needs a penetration test to test that the screw can drill and tap the thread within the specified time.

Classification
Round head: It is the most commonly used head type in the past.
Flat head: a new design that can replace round head and mushroom head. The head has a large diameter, and the periphery of the head is connected with a high-profile edge, which makes it play a driving role in high-strength torque.
Hexagon head: This is a standard type in which torque is applied to the hexagonal head. It is characterized by trimming sharp corners to close to the tolerance range. It is suitable for various standard patterns and various thread diameters.
Drive types: slotted, Philips, and pozi .
Standards: National Standard (GB), German Standard (DIN), American Standard (ANSI) and British Standard (BS)

Status Quo
At present, there are two types of self-tapping screws commonly used in China: countersunk head and pan head. Their finish treatment is usually blue zinc plating, and they are quenched during production, which is what we usually call heat treatment, so as to strengthen the hardness. The cost after heat treatment is naturally higher than that without heat treatment, but its hardness is not as high as that after heat treatment, so it depends on what products users use.

Application
Self-tapping locking screws are also used for the connection between thin metal plates. Its thread is a common thread with an arc triangular cross section, and the surface of the thread also has high hardness. Therefore, when connecting, the screw can also tap the internal thread in the bottom hole of the thread of the connected piece, thus forming the connection. This kind of screw is characterized by low screwing torque and high locking performance. It has better working performance than ordinary self-tapping screws and can be used instead of machine screws.
Self-tapping screws for wallboard are used for connection between gypsum wallboard and metal keel. Its thread is a double thread, and the surface of the thread has high hardness (≥HRC53), which can be quickly screwed into the keel without making prefabricated holes, thus forming a connection.
The difference between self-drilling screws and self-tapping screws is that elf-tapping screws have to go through two processes: drilling and tapping. For self-drilling screws, the two processes of drilling and tapping are combined. It uses the drill bit in front of the screw to drill first, and then uses the screw to tap, saving time and improving efficiency.
Pan head and hexagon head self-tapping screws are suitable for situations where the head is allowed to be exposed. Hexagon head self-tapping screws can use larger torque than pan head self-tapping screws. Countersunk self-tapping screws are suitable for occasions where the head is not allowed to be exposed.

Definition
Generally, it means that the thread is self-tapping, so that it does not need to be used with nuts. There are many types of screws, including external hexagon head, pan head, countersunk head and internal hexagon head. And the tail is generally pointed.

Function
Self-tapping screws are used for nonmetal or soft metal, without pre-drilled holes and tapping; Self-tapping screws are pointed, so as to "self-tap". Self-tapping screws can drill corresponding threads on the material to be fixed by their own threads, so that they can closely match with each other.