Patent ID: 7172483

Claim:
A method of making a metallic shell for a spark plug, the metallic shell including a multi-stepped through hole, an intermediate tubular portion, a tip end side tubular portion disposed on a tip end side of the intermediate tubular portion and a base end side tubular portion disposed on a base end side of the intermediate tubular portion, the through hole including, in the order from a base end side to a tip end side of the spark plug, a large diameter hole section, an intermediate diameter hole section smaller in diameter than the large diameter hole section and a small diameter hole section smaller in diameter than the intermediate diameter hole section, the method comprising the steps of; cutting a metal pipe that is used as a starting material to a predetermined length and thereby preparing a pipe-shaped blank; and subjecting the blank to a deformation process comprising extrusion and thereby forming the blank into the metallic shell, wherein an outer diameter of the pipe is larger than that of the tip end side tubular portion of the metallic shell and equal to or smaller than that of the intermediate tubular portion.