Miniature and instrument ball bearings are mainly divided into two basic types: deep groove ball bearings and angular contact ball bearings. Deep groove ball bearings, in turn, can be further subdivided into the following five types based on their specific design: standard type, flanged outer ring type, wide inner ring type, extended type (where the radial thickness of either the outer or inner ring is greater than that of a standard bearing), and thin-section type (where the radial thickness of both the inner and outer rings is reduced). Furthermore, deep groove ball bearings can also be classified according to their sealing and dust protection features as open, dust-shielded and sealed types.