Process variability has been used to assess the macro-geometric behaviour of materials in finish-turning. Leaded En 1A and non-leaded CS1114 free-cutting steels were compared with respect to dimensional variations in the machined diameters. The two materials differed significantly in process variability, the leaded steel causing less variability. Dimensional variation was also affected by the microstructure of the materials; it increased with the grain size of the matrix.