The friction losses of rotating disks in turbomachines are often increased by protruding bolt heads and surface imperfections, especially at the rim. This can significantly influence the heat production and flow distribution in disk cooling systems. A detailed knowledge of losses and local cooling flows is required to improve the accuracy of both performance and disk life predictions. To this end a thorough experimental study of various disk, bolt, and bolt cover configurations has been carried out. Some of the important test results are presented, and recommendations are given for minimizing windage losses. Empirical influence coefficients based on von Ka´rma´n’s equations for disk friction losses have been derived for different geometries. Furthermore, empirical correlations are proposed for the windage losses of various disk/bolt configurations.