Patent ID: 8067882

Claim:
A sealing member for a cylindrical spark plug having a metal shell with threaded ridges thereon to be screwed into a mounting hole of a combustion engine, said sealing member comprised of a piece of annular sheet material made of austenitic stainless steel or ferritic stainless steel that is folded back in a radial direction so as to form a region where at least two or more layers of the sheet material are overlapped in an axial direction, the sealing member dimensioned to be disposed around an outer circumference of said metal shell of the cylindrical spark plug, wherein the sealing member is dimensioned to be compressed in the axial direction between an annular-shaped projecting portion disposed on and projecting outwardly from the outer circumference of the metal shell and an opening circumference edge portion of a mounting hole of a combustion engine to thereby provide a seal between the projecting portion and the opening circumference edge portion when the metal shell is screwed into the mounting hole of a combustion engine, wherein the sealing member is provided around the metal shell having a nominal diameter of M12, wherein, before being mounted on the combustion engine, the sealing member satisfies the following relations: 0.2<=|[mm]<=0.5; 2<=n<=5; and 1.1 L<=x<=1.45 L (1), where the number of layers of the sheet material that constitutes the sealing member is expressed by “n” in a region having the greatest number of overlapping layers in the axial direction, where an average thickness of the sheet material is expressed by “|” [mm], where a total thickness of each layer of the sheet material in the region in which the greatest number of overlapping layers is provided is expressed by “L” [mm], and where a thickness of the sealing member in the axial direction before being compressed is expressed by “x” [mm].