A: 6204 and 6205 belong to the same 62 series deep groove ball bearings. The key difference is bore and load capacity: 6204 has a 20mm bore, 47mm OD, 14mm width; 6205 has a 25mm bore, 52mm OD, 15mm width. The 6205 carries about 25% higher dynamic load, suited for 25mm shafts under heavier duty (motors, pumps). Always size the bore to the shaft first, then verify life by load.