Semi-ground 3000® Series bearings are specially designed to provide a line of economical bearings for lighter loads than the 1600® Series bearings and speeds to approximately 2500 RPM. The 3000® Series bearings are dimensionally the same as the 1600® Series bearings, except for the precision of the inner ring (as machined tolerances). Careful heat treatment provides a uniform and exact degree of hardness for maximum life. The 3000® Series bearings are precision ground to the same close tolerances on the OD as the 1600® Series bearings with exceptional care given to the ball grooves. A ball retainer, or separator, is employed to increase the range of allowable speeds by reducing ball contact friction. Nice® Precision Deep Groove Ball Bearing, Filling Slot, Series: 3000®, 1/4 in Bore Dia, 11/16 in Outside Dia, 1 Row, 1/4 in W, Open Closure, 170 lb, 52100 Steel Bearing, Nylon Cage, 2500 RPM Maximum, 300 °F, Chrome Steel