KPO rail fastening system is quite common in the world. It is usually consist of KPO clips, screw spikes, HS bolts, Hex nuts and double coil spring washer and KD65 base plate.
The Fe 6 double spring washer is the smallest part of it. But it is quite important or the KPO rail fastening system. The wash is subject to considerable expansion and contraction. Menwhile the double Coil provides the travel necessary to maintain effective clamping force in such assemblies.
Here are details about the Fe6 double spring washer
The following are 3 artistic works of KPO railway fastening system.
The above 3 pictures are reproduced from https://grabcad.com/library/kpo-clamp-rail-fastening-system-1