Regarding radial clearance greater than normal, under what circumstances would that be good or needed; and when is it best to use the lower clearance? I searched and found this: http://bearings-catalog.ntnamericas.com/results/ball-bearing and this re clearance and preload: http://www.ntnamericas.com/en/product-support-and-training/frequently-asked-questions#b7 Compare: http://www.ntnamericas.com/en/produ...data-sheet/datasheet?pid=3121&cid=RBSRD&ctc=B to: http://www.ntnamericas.com/en/produ...data-sheet/datasheet?pid=3122&cid=RBSRD&ctc=B They are not identical. The different part numbers address the difference in radial clearance. Misalignment factor, or type of clutch plate, or wear factor for input/pilot bearing, etc?? If you know, thanks for response.