Drywall screws and thread forming self tapping screws A, AB, B, BP, C, etc. have been gradually replaced by thread rolling self tapping screws, so they are not recommended to be used in new designs. The difference between AB, B and BP is only in the tail shape. AB has a thread taper tail, B has a blunt tail, and BP has a non threaded taper tail. The center of the taper tail enters the pre drilling hole and begins to shape the thread. Thread cutting self tapping screws are in the form of BF, BP, D, F, G and T, where BF and BP are wide threads and the rest are mechanical threads.
The difference of character recognition lies in its cutting tail. Each type of cutting tail has a shape that can collect waste materials under cutting. If the self tapping screw is screwed into the blind hole (non through hole), its fragments will remain and be sealed at the bottom of the hole. However, if the through hole is penetrated, the waste will fall on the other side of the workpiece. Therefore, this must be taken into account when selecting this type of self tapping screw. The waste may cause pollution, fall into the running parts or make the electronic substrate unable to operate.
All thread rolling self tapping screws are mechanical threads, which are the same as the British American uniform coarse thread. Please refer to SAEJ81. For metric thread, please refer to SAEJ1237 and DIN7500.
There are two types of drilling self tapping screws: 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 tail are also applicable. Due to the nature of tapping, drilling and thread, drilling screws are not suitable for blind hole operations. When assembling the self drilling screw, the drill tail needs to completely penetrate the workpiece before cutting or forming the thread, so there is usually some debris. If the thread cutting type thread is used, there is inevitably debris. Therefore, this problem must be considered in practice. For BSD and CSD drilling screws, please refer to SAEJ78 and DIN7504 (wide thread). Drywall nail
Standard self tapping screw identification characters, including symbols representing thread and tail shape. Self tapping screws have one or two characters representing threads to represent mechanical threads or wide threads (SPACED). If there is identification character "B", it means wide thread screw. Those without "B" are mechanical threads. The representative characters at the tail end are used to distinguish self tapping screws from thread forming, cutting, rolling or self drilling.
The mechanical thread has the same thread angle of 60 degrees and the same pitch of coarse and fine threads as the British American unified thread. If the screw is missing or necessary after disassembly, the standard thread fastener can be used instead.
Wide thread has a thread angle of 60 degrees, but its pitch is wider. Because of its wide pitch, its thread is steeper, so its thread lead is larger than that of mechanical thread. Another kind of thread is specially used on plastics. Its thread angle is 48 degrees, commonly known as PT thread.
