How to choose self drilling and self tapping screws

Introduction to self drilling and self tapping screws

Tapping Screws

Self drilling self tapping screws, also known as "Drilling screws with tapping screw threads", are drilling screws with self tapping threads. Here we need to focus on the two words "drilling", which means that the difference between self drilling self tapping screws and self tapping screws is that pre drilled holes do not need to be drilled. Before installing self tapping screws, it is necessary to drill pre drilled holes, and in order to achieve good fitting results, the tolerance requirements for pre drilled holes of self tapping screws are also relatively strict. Self drilling self tapping screws can be assembled without the need for pre drilled holes. To summarize, the characteristic of self drilling self tapping screws is the simultaneous one-time operation of drilling, tapping, and tightening. Greatly reduces assembly costs and improves assembly efficiency.

Thread characteristics

The thread pitch and profile angle of self drilling self tapping screws are the same as those of self drilling screws, but the difference is that the thread end of self drilling self tapping screws is designed with a "pointed tail" similar to a drill bit, which is used for drilling. Therefore, in the fastener industry, it is common to refer to self drilling self tapping screws as "drill tail screws".

Head shape
Self drilling self tapping screws come in various head forms according to standards, including countersunk head, semi countersunk head, pan head, slotted hexagonal flange, hexagonal flange, and hexagonal flange.

Q:

Why does the self drilling and self tapping nail head type not have an outer hexagon?

The main reason is that the external hexagonal head has a large force area and can withstand a large installation torque, When installing self drilling self tapping screws, it is necessary to rely on the pointed tail of the thread to self drill, which may cause the screw head to break due to excessive torque during high-speed installation of electric installation tools. Therefore, the head form of self drilling self tapping screws is designed as a hexagonal flange or hexagonal flange, with a larger contact area between the flange and the flange. When the screw is installed in place, it is easier to detect and stop applying torque in a timely manner.

Twisting structure
The wrench structure is a force bearing structure designed to achieve the assembly of threaded connections and ensure the smooth installation of screws. It can be divided into external wrench structures and internal wrench structures. The following figure shows the common tightening forms of self drilling self tapping screws, where the cross groove and cross groove belong to the internal tightening structure, the hexagonal head belongs to the external tightening structure, and the slotted hexagonal head takes into account both external and internal tightening structures.

Q:

Why is there no slotted and twisted structure for self drilling and self tapping screws?

This is because self drilling self tapping screws require drilling holes. In order to ensure high-speed installation of electric installation tools, the screwing structure of self drilling self tapping screws must be able to withstand large impact forces. The positioning point and force area of the separate slotted screwing structure are small, which is prone to tool slipping or screw damage during high-speed installation, which is not safe and affects assembly efficiency.