Vertical rotational movements in spherical bearings are accomplished through sliding between the spherical cap liner and the spherical sliding plate. Often,because the rotation center of the bearing does not coincide with the rotation center of the superstructure,a second sliding surface is formed between the upper bearing plate and the flat sliding plate. Depending on the relative position of the superstructure and the bearing's rotation center,the direction of spherical rotation can be either the same as or opposite to the direction of planar sliding.