1-1. Purpose and selection

The purpose of fit is to prevent harmful sliding between two mating bodies, by securely fastening a bearing ring, which rotates under loads, on the shaft or housing.
This harmful sliding is called creep. It may induce excessive heating, wear in the contact area of the mating surfaces, ingress of wear debris into the bearing, vibration, and other unwanted phenomena.
 
To determine what class of fit is optimal, examine the following:
1) The characteristics and sizes of loads
2) Temperature distribution during rotation
3) Bearing internal clearance
4) The material, finishing, and strength of the shaft and housing
5) Mounting and dismounting methods
6) Whether shaft thermal expansion needs to be accommodated between the mating surfaces of the fit
7) Bearing type and dimensions