Denso Racing Spark Plug IU01-34. Manufacturer Part Number 5737. Denso Iridium Racing Spark Plugs offer the ultimate in strength, performance and value. Ultra fine 0.4mm Iridium alloy centre electrode offers the ultimate performance whilst the solid platinum, laser welded ground electrode offers extreme strength and resistance to vibration damage for high revving engines. Supplied in individual protective plastic case. Please note that the last 2 digits of the part number indicate the heat range where 24 is the warmest and 34 is the coldest. Made in Japan.