Denso iridium racing spark plugs feature a special hardened insulator that is 20% stronger for hard core racing applications. 100% platinum 0.8mm ground electrode reduces wear under severe driving or race conditions. Ultra-fine 0.4mm diameter iridium alloy center electrode reduces voltage requirements, greatly improving ignition performance. Patented self-cleaning electrode design. Silicone oil coated insulator to repel moisture and carbon buildup. Handles extreme compression and boost levels. Machine rolled threads prevent seizing or cross threading during installation and removal. 100% pre-fired to assure the highest quality possible. Purified alumina powder insulator provides exceptional strength and thermal conductivity. Five rib insulator prevents flashover. Copper-glass seal bonds center electrode and insulator for a gas-tight seal.