Technology >>Interchangeability ofScrews/Nuts & Tightening Tools
螺絲、螺帽與鎖緊用工具的互換性
The Murphy screws principle says: “If you are looking for four identical screws, youwill definitely find only three.”In such a case, the question of the interchangeability of the screws and the tightening
tools is legitimate. However, as we will see below, not all bolts/nuts and tightening
tools are interchangeable. In this article, we will try to specify it in concrete cases.

Some Practical Examples
A frequent source of errors is the cross groove on screws. Many people, evenprofessionals, think that there is a universal type of cross slot and they can use withany cross screwdrivers. Despite their similar appearance, these two systems are notinterchangeable (Fig. 1). The expert has surely already noticed why. The reason forthis is the different shapes of the glossy contact surfaces of the PH (Phillips) and PZ(Pozidrive) systems. Interchanging them could damage not only the bit itself, butalso the tightening groove on the screw. And the worst solution would be to use a flatscrewdriver for a cross slot. Unfortunately, this also happens in practice.

Fig. 1Another example of prohibited interchange
is incorrect orientation of fastening nuts ofvehicles wheels (Fig. 4). Wrong assembly
direction can cause loosening of the wheel
during movement. Official statistics do notshow the full truth, because there are not many
drivers, who will admit that loosening of thewheel was their fault.
Example of possible interchange is trilobular
screw (Fig. 5). Special property of this typeof trilobular screw is the ability to makeHardware & Fastener Components - no.56/2022

Fig. 2 Wrench & screw

As you can see in Fig. 2, screws are often tightened by popular French keys. It is
important to highlight though that it is not advised to use this assembly tool multiple
times, because the edges are being damaged quickly (transmission of torque is done
only trough the edge). It is nicely demonstrated by Fig. 3a. For this reason, tightening
with arc-screw (Fig. 3b) is much better (transmission of torque is done throughbigger surface).

a.

b.

Fig. 3060

Fig. 4Fig. 5 Trilobular screwTechnology >>Fig. 6 Screw with threads dedicated to plastic

Fig. 7 Cracks in the plastic

counter threads during assembly by rolling - without making splinters. It is interchangeable with any other metrical screw of the same
diameter. Trilobular screws can in extreme cases be used as a tool to make internal threads.
The Screw with threads dedicated to plastic (Fig. 6) is not interchangeable by any other. In the case where it happens, cracks canemerge in the plastic (Fig. 7).

Conclusion
As we have seen, there are many ways to use screws and screw drivers wrongly. There are many cases of impossible
interchangeability. Not knowing about interchangeability can be damaging to both screws and screw drivers, which can further leadto collapse of construction units. A common example is bad application of fastening screws/nuts of automobile wheels, which can, forthe reason of poor application of tightening moment or use of bad strength class, lead to very dangerous loosening of the wheel.

Hardware & Fastener Components - no.56/2022

Article by Jozef Dominik and Dominik Makuka / Copyright owned by Fastener World061