This paper discusses how periodic revision of tapered roller bearing ratings and reappraisal of the rating formula used by The Timken Roller Bearing Co. are accomplished by a continuing testing program on standard product bearings. An extensive sampling plan, designed to include bearing product up to 6 in. O.D. from both domestic and overseas manufacturing plants, is fully described. A review of recent fatigue tests on over 5000 bearings illustrates the experimental basis for the rating increases announced in 1967. Limited bearing fatigue tests conducted under conditions of lubricant, temperature, and speed different from those used for establishing bearing ratings indicate the need for determining rating adjustment factors to compensate for the influence of the application environment.