Abstract: A two-piece spark plug includes an electrically conductive outer housing including a cylindrical member having an outer wall and an inner wall, the inner wall defining a passage through the outer housing, and a plug member releasably coupled within the outer housing and including an axial electrode and an electrically insulating insulator element encircling the axial electrode, the axial electrode having a first end for connection to an electrical source and a second end for connection within a combustion chamber, and the insulator element having a circumferential first groove and adapted to be positioned within the passage of the outer housing such that a gas-tight seal is formed between the insulator element and the inner wall of the outer housing.