Abstract: By use of V notched round bars with differenttheoretical stress concentration factors as finite element models (FEM)of tensile screw threads, stress intensity factors(SIF) of surfacecracks of screw threads are calculated. A universal SIF formula onsurface cracks of screw threads is proposed. In addition, bycomparison of the SIF results of M22\times1.5 screw thread in this paper withexperimental results, the effectiveness of the SIF results areshown.