Used as a spring washer on Sole Ellipticals E35 and higher. This goes in between the pedal arm and cross bar (crank arm) connection. In this case, it gets paired with a nylon wave washer. Without it, there will be some lateral play in the machines movements.
On some Sole Elliptical models, it is used as a spring washer between and handle bar and the console mast.
If you have an older Sole Elliptical that has developed a deep single or double thud per rotation, add this wave washer between the drive axle spacer and the inside bearing. (Estimated repair time to accomplish this is 120min)