Method of producing insulator for spark plug

A method of producing a cylindrical insulator for insulating, in a spark plug, a housing having a ground electrode and a central shaft having a center electrode from each other, the method comprising:

• a molding step of forming ceramic powder filled in a cavity into a compact, the cavity defined by a mold configured to form an outer face of the insulator and a molding pin placed in the mold and configured to form an inner face of the insulator;
• a first removal step of removing, from the mold, the compact with the molding pin placed therein;
• and
• a second removal step of removing the molding pin from the compact,
• wherein the molding pin has at least one recess formed in an outer cylindrical surface thereof partially along a circumferential direction of the outer cylindrical surface,
• in the first removal step, the compact has at least one protrusion formed in the at least one recess of the molding pin, and the at least one protrusion is locked in the at least one recess, thereby allowing the compact to be removed with the molding pin from the mold, and
• in the second removal step, the molding pin is turned or rotated in the circumferential direction about the compact, causing the at least one recess to cut the at least one protrusion from the compact, and thereafter the molding pin is removed from the compact.