HKS M-Series Super Fire Racing spark plugs are high performance Iridium plugs designed to handle advanced levels of tuning and provide Improved ignition performance, durability and anti-carbon build-up Features 0.6mm Iridium Alloy Center Electrode Iridium Alloy Center Electrode reduces voltage requirement as well as improving ignition performance and durability.Outer Electrode with Platinum Chip The Outer Electrode incorporates a square platinum chip which improves durability, and when combined with the iridium center electrode boosts ignition performance.Short Type Outer Electrode (Anti-Vibration) The outer electrode has been shortened and engineered with the ideal shape to decrease weight for resistance against vibration.