What is the form of self-tapping screws?

Update:10-08-2018
Summary:

Standard self-tapping screws recognize characters, incl […]

Standard self-tapping screws recognize characters, including symbols that represent the shape of the thread and tail. Self-tapping screws have one or two characters representing the thread to represent a mechanical thread or a wide thread (SPACED). If the character "B" with the identification character is represented by a wide threaded screw. No "B" is represented by a mechanical thread, and the tail end represents a character used to distinguish the self-tapping screws for thread forming, cutting, rolling or self-drilling. The mechanical thread has the same 60 degree thread angle and coarse and fine thread as the Anglo-American thread. If the screw is missing or needed after disassembly, it can be replaced by a standard threaded fastener. The wide thread has a thread angle of 60 degrees but its pitch is wider, and because of its wide pitch, its thread is steeper and its thread lead is larger than the mechanical thread. There is also a thread specially used for plastics with a thread angle of 48 degrees, commonly known as PT screw.

Thread forming self-tapping screws A, AB, B, BP, C and other types have gradually been replaced by thread rolling self-tapping screws, so it is not recommended in the new design. AB, B, BP differ only in the shape of the tail, AB has a threaded tail, B has a blunt tail, BP has a non-threaded cone tail, the center of the tip enters the pre-drilled hole and begins to shape the thread. Thread cutting self-tapping screws are available in the form of BF, BP, D, F, G and T. BF, BP are wide threads and the rest are mechanical threads. The distinguishing character is the cutting tail. Each cutting tail has a shape that collects the scrap under cutting. If the tapping screw is screwed into a blind hole (a hole that does not pass through), the debris will remain and seal to the bottom of the hole. However, if you break into the through hole, the waste will fall on the other side of the workpiece. Therefore, it is necessary to consider this when selecting this type of self-tapping screws.

The waste may cause pollution, fall into the running parts or make the electronic substrate inoperative. All threaded self-tapping screws are mechanical threads, the same as the British and American unified thread coarse teeth, please refer to SAE J81 regulations. For metric threads, please refer to SAE J1237 and DIN7500. The self-tapping screws of the drill tail have two types: cutting wide thread BSD and mechanical thread CSD. There are also special thread types, including high and low double threads, and a variety of tapping tails are also suitable. Due to the nature of the drill tail and the thread, the self-drilling screw is not suitable for blind hole operations. When assembling the self-drilling screw, the drill tail needs to completely penetrate the workpiece to cut or shape the thread, so there will usually be some debris. If the thread cutting type thread is used, it is even more necessary to have debris. Therefore, it must be considered practically. This question. Please refer to SAE J78 and DIN7504 (wide thread) for BSD and CSD self-drilling screws.