Fit

A fit describes the dimensional relationship between a bearing ring and its seat – inner ring to shaft, outer ring to housing bore. Since bearing boundary dimensions are standardized to ISO tolerances, the fit is determined solely by the shaft and housing tolerance zones, producing clearance, transition or interference conditions.

Selection depends primarily on the load case: the ring subjected to circumferential load needs a tight fit, while the point-loaded ring may sit looser. Size, load magnitude, temperature and required running accuracy also matter. A fit that is too loose causes ring creep and fretting corrosion; one that is too tight reduces internal clearance, so fit and clearance class must always be considered together.