Denso OE Iridium Spark Plug SK20R-P13. Manufacturer Part Number 3298. Denso OE Iridium Spark Plugs use a performance copper core to improve conductivity of electrical current. The central electrode is tipped with Iridium alloy to greatly extend service life and allow a smaller electrode diameter of 0.6mm, this improves performance and efficiency of the ignition system. Many designs also use a Platinum chip in the ground electrode, it's not uncommon for service life to be 100,000 miles for these plug types. These spark plugs are specified by the manufacturer for modern engines which have extremely long service intervals or where access to change the spark plugs is difficult. Made in Japan.