Generally, the shaft is supported by two bearings in the radial and axial directions. At this time, the bearing on one side is called a fixed-side bearing, which bears both radial and axial loads. The effect of relative axial displacement between the two. The other side is called the free side, and it can only move in the axial direction because of the radial load. This solves the problem of the expansion and contraction of the shaft due to temperature changes and the gap between the bearings.
For fixed-side bearings, you need to choose a bearing that can be moved axially with a rolling surface (such as a cylindrical roller bearing) or with an assembly surface (such as a radial ball bearing). In the case of relatively short shafts, when the fixed side is not significantly different from the free side, a bearing that moves only in one direction (such as a radial thrust ball bearing) is used.
