ESDU 86028 discusses the effect of keyway design on the stress distribution, stress concentration and, hence, on fatigue strength. The effect of fit is considered and types of failure by crack propagation illustrated. Data are presented on the fatigue strength of a shaft with the keyway in bending, and a shaft loaded through the key in torsion. Stress concentration values as a function of keyway geometry are also presented for a shaft with the keyway in bending, and a shaft loaded through the key in torsion. A worked example illustrates the use of the data.