The spring force results in FEM loads distributed among two annular faces, each belonging to one part. This load distribution comes from the assumption that the ends of the spring are closed and ground1, leading to a uniform annulus-shaped load distribution.
The videos below depict the action FEM loads applied to the base mesh (left) and the reaction FEM loads acting on the mass mesh (right). The base is grounded. The grounded geometries are the two annular faces around the bottom sides of the two symmetrical holes.