1 miniature bearings - bearings with a nominal outside diameter range D < 26mm;
2 small bearings - bearings with a nominal outside diameter range of 26 ≤ D < 60mm;
3 medium and small bearings - bearings with a nominal outer diameter range of 60 ≤ D < 120mm;
4 medium and large bearings - bearings with a nominal outer diameter range of 120 ≤ D < 200mm;
5 large bearings - bearings with nominal outer diameters ranging from 200 ≤ D < 400 mm;
6 Extra large bearings - bearings with a nominal outer diameter range of 400 ≤ D < 2000 mm;
7 heavy large bearings - bearings with nominal outer diameter size range D ≥ 2000mm;