Wave washer of iron material has a perfect size for bearings, but I bought this for stainless steel materials but I wish it would be a little more rich in size. This is a bit small, so it's hard to incorporate it.
It is used on the threaded bearing surface when installing the pedal to prevent scratches and galling of the crank. Because there is a reaction force in the washer itself, I think that it will also prevent loosening of screws. Since the inner diameter dimension is φ 14.5 (+ 0.3 / - 0.15), it is perfect for the thread of φ 9/16 inch (≈ φ 14.3).