The effect of stress distribution at rupture is discussed. By the author's theory, the rupture of a thin hollow cylinder occurs when the principal stress attains a definite value σ_B, the tensile strength of the material under uniform stress. For a solid cylinder of ordinary cast iron, [numerical formula] where, d=diameter of the cylinder, and M_B=torsional moment at rapture. As for the strain, the solid cylinder can endure twice or more the strain of thin hollow cylinder. Experiments were carried out ; theory and experiments conform very closely.