Iridium Power™ Spark Plug (5338) by Denso®. Iridium Ultimate Endurance and Power – Performance Upgrade with World’s Smallest Center Electrode (0.4mm Iridium and 0.7mm Platinum Twin-Tip Technology) & Tapered Tip Patented U-Groove Design & Patented Ir Alloy (90% Ir). Iridium Power™ best demonstrates its performance improvement during acceleration. The world’s smallest center electrode and specially shaped ground electrode delivers maximum spark energy while withstanding temperatures greater than 4000º F. These features combine to achieve higher ignitability and require lower spark voltage than ever before. As a result, acceleration improves in comparison with normal plugs.