ESDU 74027 gives curves for the peak-to-valley surface roughness below which improvement of the surface finish will not affect the fatigue limit@ and also gives curves for the effect on fatigue limit of increasing the peak-to-valley surface roughness above that value. The curves are a function of the steel tensile strength and they are compared with over 100 experimental points extracted from the literature. The likely value of roughness associated with various finishing techniques from die cast through milling to superfinish is indicated@ and the relationship between centre-line average roughness and the peak-to-valley roughness used on the graphs is explained.