A: Both are single-row tapered roller bearings handling radial and single-direction axial loads. 30205: 25mm bore, 52mm OD. 30206: 30mm bore, 62mm OD. The 30206 offers higher load and life for larger shafts and heavy duty (wheel hubs, gearboxes). When used in pairs, watch the mounting orientation (face-to-face or back-to-back).