Single row deep groove ball bearings are manufactured as open type (unsealed), sealed and shielded, the most popular sizes of deep groove ball bearings are also produced in sealed versions with shields or contact seals on one or both sides, the bearings with shields or seals on both sides are lubricated for life and are maintenance free. A sealed bearings seals has contact on the bearings inner and outer, a shielded bearings shield has contact on the outer only, and Shielded bearings are primarily intended for applications where the inner ring rotates. If the outer ring rotates, there is a risk that the grease will leak from the bearing at high speeds.
