A standard internal clearance (CN) is suitable for the operation of the bearing in case of ordinary temperatures and for customary fits. An increased internal clearance (C3) is recommendable in case of high temperature gradients between the rings or in case of fixing the bearing through a press fit.
Plastic seals (RS/2RS) have the optimum sealing action with increased friction. Metal seals (Z/ZZ) are suitable for higher speeds, but they have a limited sealing action as they seal contactless. Open, seal-less bearings are suitable for extremely high speeds and - furthermore - they can be regreased easily. However, they are more susceptible to soiling.