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Thread type of self-tapping screws


Thread type: Standard self-tapping screw identification characters, including the symbols representing the thread and tail shape. Self-tapping screws have one or two characters representing the thread to represent mechanical threads or wide threads (SPACED). If there are identification characters" B" represents a wide threaded screw. The one without "B" represents a mechanical thread. The tail end represents the character used to distinguish self-tapping screws as thread forming, cutting, rolling or self-drilling.

The mechanical thread has the same thread angle of 60 degrees and the same pitch of the coarse and fine threads as the unified thread of the United Kingdom and the United States. If the screw is lost after disassembly or if necessary, it can be replaced by a standard threaded fastener.

Wide thread has a thread angle of 60 degrees but its pitch is wider, and because of its wide pitch, its thread is steeper, so its thread lead is larger than mechanical thread. There is another kind of thread specially used on plastics, The thread angle is 48 degrees, commonly known as PT screw.

Thread forming self-tapping screws A, AB, B, BP, C and other types have been gradually replaced by thread-rolling self-tapping screws, so it is not recommended to use them in new designs. The difference between AB, B, BP is only in the shape of the tail. AB has a threaded cone tail, B has a blunt tail, and BP has a non-threaded cone tail. The center of the pointed tail enters the pre-drilled hole and begins to form the thread. Thread cutting self-tapping screws have BF, BP, D, F, G And T and other forms, BF, BP are wide threads, and the rest are mechanical threads.

The difference between the identification characters is the cutting tail. Each cutting tail has a shape that can collect the scraps from the cutting. If the self-tapping screw is screwed into the blind hole (non-through hole), the debris will remain and be sealed at the bottom of the hole However, if the through hole is tapped, the waste will fall on the other side of the workpiece. Therefore, this type of self-tapping screw must be considered when choosing this type of self-tapping screw. The waste may cause pollution, fall into the running parts or make the electronic substrate impossible Operation.

All thread-rolled self-tapping screws are mechanical threads, which are the same as the coarse thread of the British and American unified threads, please refer to SAE J81 regulations. For metric threads, please refer to SAE J1237 and DIN7500 regulations.

Self-drilling self-tapping screws have two types of cutting wide thread BSD and mechanical thread CSD. There are also special thread types, including high and low double threads, and various tapping and drilling are also applicable. Because of the nature of tapping and threading, self-drilling screws It is not suitable for blind hole operations. When assembling self-drilling screws, the drill tail must penetrate the workpiece completely before the thread can be cut or formed, so there will usually be some debris. If thread cutting threads are used, it will inevitably be broken. Chips. Therefore, it is necessary to consider this issue practically. For BSD and CSD self-drilling screws, please refer to SAE J78 and DIN7504 (wide thread).

The most important thing about the thread of a se

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