Self-tapping screws structure and characteristics

Each self-tapping screw consists of three parts: the head, the stem and the end of the stem. Each self-tapping screw has four major components: head shape, wrenching, thread type, and end form.
1. Head shape
The shape of the head is varied. Round head (semicircular head), oblate head, round head flange (with pad), flat head flange (with pad), pan head, pan head flange (with pad), countersunk head, semi-recessed head, Cylindrical head, spherical cylindrical head, horn head, hexagonal head, hexagonal flange head, hexagonal flange (with pad) head.
2. Twisting method
The wrenching method refers to the way of twisting the screw head when installing and tightening the screw. The basic methods are the outer wrench and the inner wrench. In general, the outer wrench is more torque than any type of inner wrench (inner groove). External wrench: hexagonal, hexagonal flange face, hexagonal flange, hexagonal flower shape, etc.; internal wrench: slot, cross slot H, cross slot Z, cross slot F, square slot, composite slot, inner flower Key, hexagonal flower shape, inner triangle, inner hexagon, inner 12 angle, clutch groove, six-blade groove, high torque cross groove, etc.
3. Thread type
There are a wide variety of threads, including self-tapping threads (wide thread), machine threads (ordinary threads), drywall nail threads, fiberboard nail threads, and other special threads. In addition, the thread can be divided into single lead (single head), double lead (double head), multi-lead (multi-head) and high and low double-head thread.
4. End form
The end form mainly has two kinds of cone ends and flat ends. However, depending on the use, a groove, a groove, a slit or a portion similar to a drill shape having a cutting function can be processed at the screw-in portion of the tip. In some standards, the same is the tapered end or the flat end, and there are also different forms such as the round end.

Although there are many types of self-tapping screws, they all have the following in common:
(1) It is generally made of carburized steel (99% of total production). 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, and stainless steel self-tapping screws must be solid solution hardened. In order to achieve the mechanical properties and performance properties required for the self-tapping screws.
(3) The product has high surface hardness and good core toughness. That is, "inner soft outside just." This is a major feature of the performance requirements of self-tapping screws. If the surface hardness is low, it will not be screwed into the base; if the core has poor toughness, it will not be used if it is broken. Therefore, "inner flexible steel" is a very important requirement for self-tapping screws to meet the performance.
(4) The surface of the product needs surface protection treatment, generally electroplating treatment. Some products have to be phosphate treated (phosphating), such as wallboard self-tapping screws are mostly phosphating.
(5) Production by cold heading process. It is recommended to use a high speed cold heading machine and a high speed thread rolling machine or a high speed planetary thread rolling machine. The emphasis on high speed is to ensure product quality. Only the head of the self-tapping screw produced by the high-speed machine is formed, and the thread quality is high.

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