Answer
Shim ends are flat, circular sections at the top and bottom of a multi-turn wave spring. They are formed by gradually reducing the wave height to zero at the ends of the coil. Shim ends provide a $360^\circ$ contact surface, unlike standard wavy ends which only contact at the peaks. This is beneficial in two ways: first, it distributes the load more uniformly over the mating part, which is critical when the mating part is made of a softer material like aluminum or plastic that could be 'notched' by peak loading. Second, it simplifies assembly by providing a stable, flat base that prevents the spring from tilting during installation. In aerospace bearings, shim ends ensure that the pre-load is perfectly axial, preventing parasitic torques or misalignments.
