Denso Iridium Spark Plug - IWF22 5379Six times harder than platinum, iridium doesnt melt in temperatures up to 4,000F Because the iridium electrodes of these plugs can be shrunk to only 0. 4mm, voltage requirements decrease while firing performance improves 360 laser welding of electrode provides a seal that resists wear even in the worst conditions Ground electrode features a tapered cut and U groove that form a large volume area for the flames center