Spring failures were investigated in this study. A seam that extended more than 0.05 mm below the wire surface was revealed and the fatigue-fracture front progressed downward from several origins. A crack that is triangular in outline was produced by each of the fronts. This was reported to have occurred when the fracture plane changed to an angle with the wire axis in response to the torsional strain. The spring failure was concluded to have originated at the seam.