Self-tapping screws are generally fingertip, coarse teeth, and hard wood screws, as well as aluminum alloy and plastic. A special self-tapping screw for opening metal holes is called a tap. Self-tapping screws are used for non-metallic or softer metals, without bottom holes and tapping; Self-tapping screws are pointed, so as to “self-tapping”; Ordinary screws are flat headed, the same thickness.

Self-tapping screw means that the hole is drilled without tapping the hole, the screw is different from the general, the head is pointed, the tooth distance is relatively large, and the chip free tap is a bit like, you can screw directly into the hole without tapping the teeth, metal and plastic are usually used this method.

Self-tapping screws can be consolidated on the material, relying on its own thread, the consolidated body will “tap – drill, squeeze, press” out of the corresponding thread, so that they are closely matched with each other.

Self-tapping screw is a kind of screw with a drill bit, which is constructed by a special electric tool, drilling, tapping, fixing and locking are completed at once. Self-tapping screws are mainly used for the connection and fixing of some thin plate parts, such as the connection of color steel plate and color steel plate, the connection of color steel plate and purlin, wall beam, etc., and its penetration capacity is generally not more than 6mm, and the maximum is not more than 12mm. Self-tapping screws are often exposed to the outdoors and have strong corrosion resistance; The rubber sealing ring can ensure that the screw does not seep water and has good corrosion resistance.

Self-tapping screws are usually described by three parameters: screw diameter series, number of threads per inch length and screw length. There are 10 and 12 screw diameter classes, and the corresponding screw diameters are 4.87mm and 5.43mm respectively. The number of threads per inch length has 14, 16, 24 three levels, the more the number of threads per inch length, the stronger its self-drilling ability.
From beginning to end, the self-tapping screw is composed of three parts: the head, the rod and the end of the rod. The composition of each self-tapping screw has four major elements: head shape, screw mode, thread type and end type.

Head shape – There are a variety of head shapes. There are round head (half round head), flat head, round head flange (with pad), flat head flange (with pad), pan head, pan head flange (with pad), countersunk head, semi-countersunk head, cylindrical head, spherical cylinder head, horn head, hexagonal head, hexagonal flange head, hexagonal flange (with pad) and so on.
Thread types – There are many kinds of threads. There are self-tapping thread (wide tooth thread), machine thread, drywall screw thread, fiberboard screw thread, and some other special thread. In addition, the thread can be divided into single lead (single head), double lead (double head), multiple lead (multiple) and high and low teeth double head thread.
Although there are many types, they all share the following key characteristics:

(1) It is generally made of carburized steel (99% of the total product). It can also be made of stainless steel or non-ferrous metals.

(2) The product must be heat treated. Carbon steel self-tapping screws must be carburized, stainless steel self-tapping screws must be solid solution hardening treatment. In order to make the self-tapping screw to meet the requirements of the standard mechanical properties and performance.

(3) The product surface hardness is high, the core toughness is good. That is, “soft inside but tough outside.” This is a major feature of the performance requirements of self-tapping screws. If the surface hardness is low, it cannot be screwed into the matrix; Such as the core toughness is poor, a twist will be broken, can not be used. Therefore, “soft inside and rigid outside” is a self-tapping screw to meet the requirements of performance.

(4) The surface of the product needs surface protection treatment, generally electroplating treatment. The surface of some products needs to be treated with phosphate (phosphating). For example: wall panel tapping screws are mostly phosphating.

(5) Production by cold heading process. It is recommended to use high-speed cold heading machine and high-speed wire rolling machine or high-speed planetary wire rolling machine to ensure product quality. The head of the self-tapping screw produced in this way is well formed and the thread quality is high.