Autolite 23 - Spark Plug (Pack of 4) Copper-glass seal bonded insulator, terminal post, and center electrode provide a tight seal that is 100 percent leak-proof Multi-rib insulator reduces danger of "flash-over" to prevent misfires Full copper core electrode improves heat transfer and optimizes plug life Copper core center electrode provides higher thermal conductivity Features high alumina ceramic for high dielectric strength and steel shell for installation robustness