These Ball Bearings are made from SAE 52100 Chrome Steel to sustain radial, thrust and combined loads proportionate to the capacities of the small shafts for which they are designed. Especially suitable for use in fractional horsepower motors, small appliances, precision instruments and similar devices, these double-shielded Bearings are electric motor quality for applications requiring extra-quiet performance. Item Diameter tolerance is +.000/-.005 inches. Bore diameter tolerance is +.0000/-.0003 inches.