A spark plug (80) having a center electrode (82) with a cylindrical body and having a tip (84) at one end and a terminal (123) near the other end with an insulator (86) extending around the center electrode (82). A ground shield and retainer unit extends around the insulator (86) and includes a threaded portion (88) near one end and a ground electrode (85) near the other end, having a portion thereof aligned with the center electrode tip (84) to form a spark gap, with a sealing portion (92) disposed therebetween for sealing the engine combustion chamber from the outside environment when the spark plug (80) is installed. The ground shield and retainer unit can be formed from two parts (88,90) which are deformed during manufacturing to be in mechanical engagement and securely holding the insulator (86) in place. The spark plug (80) can also have two or more center electrodes (82,84) with two or more corresponding ground electrodes (83,85) projecting from the ground shield (90).