In this investigation the stress concentration factor was evaluated for a hollow stepped shaft with variable wall thickness and two fillet sizes. Electric strain gages of the SR-4 type were employed to measure strains in the fillet section. Values of the stress concentration factor were determined with the ratio of inside to outside diameter ranging from 0.25 to 0.625. A decreasing relation was established between stress concentration and the internal diameter. A satisfactory method of positioning gages accurately on the complex fillet surface was developed. This method featured an intermediate steel template with positive referencing. / M.S.