Official Answer
Answer
Shim ends are flat, circular sections at both ends of a multi-turn wave spring. They provide a $360^{\circ}$ flat contact surface for the mating components, as opposed to the point contact of a standard 'plain end' wave. This is crucial for distributing the spring load evenly over the entire circumference of the mating seal or bearing race. During installation, shim ends prevent the 'digging in' of the spring ends into softer housing materials (like aluminum). From a design perspective, shim ends also provide a more consistent spring rate $k$ because the boundary conditions at the ends are more clearly defined and less sensitive to the orientation of the spring.
