The objective of this document is to limit the number of sizes of radial bearings sufficiently to ensure economical manufacture on the one hand, and to provide a sufficient number of sizes to meet current and future requirements of bearing users on the other. These requirements are comprehensive and differentiated. Therefore, a wide range of numerically defined sizes and proportions must be considered in this document, and the possibility that it may even be extended according to the guidelines in Annex A must be taken into account. ISO standardized tapered roller bearings, radial insert ball bearings and some types of needle roller bearings, as well as precision bearings for instruments, do not conform to this document, since the dimensions given here are not considered optimal for the bearings in question. This document specifies the preferred main dimensions of radial bearings of diameter series 7, 8, 9, 0.1, 2, 3 and 4.