An internal combustion engine ignitor (10; 110; 210; 310; 410; 510) configured for attachment in an opening of a cylinder head, comprising: an insulator (14; 114; 214; 514) extending between a nose end and a terminal end; an electrode received in said insulator (14; 114; 214; 514) and extending outwardly from said nose end; a terminal received in said insulator (14; 114; 214; 514) and extending outwardly from said terminal end, said terminal being configured in electrical communication with said electrode; a metal shell (20; 120; 220; 320; 420; 520) surrounding at least a portion of said insulator (14; 114; 214; 514) and being free of external threads for attachment to the cylinder block; and a tube (30; 130; 230; 330; 430; 530) having a lower end receiving said terminal end of said insulator (14; 114; 214; 514) therein, said tube (30; 130; 230; 330; 430; 530) extending to an upper end opposite said lower end (52; 552), said lower end (52; 552) of said tube (30; 130; 230; 330; 430; 530) being configured to compress said shell (20; 120; 220; 320; 420; 520) into fixed position within the opening of the cylinder head; and a mount flange attached to said upper end of said tube (30; 130; 230; 330; 430; 530) and having a planar mounting surface configured for attachment to an upper surface of the cylinder head, said mount flange being configured for compressing said lower end (52; 552) of said tube (30; 130; 230; 330; 430; 530) into abutment with said shell (20; 120; 220; 320; 420; 520); wherein said shell (20; 120; 220; 320; 420; 520) has a radially outwardly extending flange (28; 128; 228; 328; 428) and said lower end (52; 552) of said tube (30; 130; 230; 330; 430; 530) is configured to apply a compressive force against said flange (28; 128; 228; 328; 428); the internal combustion engine ignitor (10; 110; 210; 310; 410; 510) further comprising a cover attached to said mount flange, said cover providing a sealed environment within said cover and within said tube (30; 130; 230; 330; 430; 530); wherein the mount flange has a fill opening for the introduction of pressurized inert fill gas into said sealed environment, said fill opening being configured to be sealed closed after the introduction of the pressurized inert fill gas. an insulator (14; 114; 214; 514) extending between a nose end and a terminal end; an electrode received in said insulator (14; 114; 214; 514) and extending outwardly from said nose end; a terminal received in said insulator (14; 114; 214; 514) and extending outwardly from said terminal end, said terminal being configured in electrical communication with said electrode; a metal shell (20; 120; 220; 320; 420; 520) surrounding at least a portion of said insulator (14; 114; 214; 514) and being free of external threads for attachment to the cylinder block; and a tube (30; 130; 230; 330; 430; 530) having a lower end receiving said terminal end of said insulator (14; 114; 214; 514) therein, said tube (30; 130; 230; 330; 430; 530) extending to an upper end opposite said lower end (52; 552), said lower end (52; 552) of said tube (30; 130; 230; 330; 430; 530) being configured to compress said shell (20; 120; 220; 320; 420; 520) into fixed position within the opening of the cylinder head; and a mount flange attached to said upper end of said tube (30; 130; 230; 330; 430; 530) and having a planar mounting surface configured for attachment to an upper surface of the cylinder head, said mount flange being configured for compressing said lower end (52; 552) of said tube (30; 130; 230; 330; 430; 530) into abutment with said shell (20; 120; 220; 320; 420; 520); wherein said shell (20; 120; 220; 320; 420; 520) has a radially outwardly extending flange (28; 128; 228; 328; 428) and said lower end (52; 552) of said tube (30; 130; 230; 330; 430; 530) is configured to apply a compressive force against said flange (28; 128; 228; 328; 428); the internal combustion engine ignitor (10; 110; 210; 310; 410; 510) further comprising a cover attached to said mount flange, said cover providing a sealed environment within said cover and within said tube (30; 130; 230; 330; 430; 530); wherein the mount flange has a fill opening for the introduction of pressurized inert fill gas into said sealed environment, said fill opening being configured to be sealed closed after the introduction of the pressurized inert fill gas.