Denso (5364) IU31 Iridium Power Spark Plug, (Pack of 1) 0.4 mm iridium center electrode: world's smallest diameter that maximizes firing potential U-groove and taper cut ground electrode: provides faster spark flame growth and lessens heat quenching DENSO patented 360 degree laser welding process: ensuring exceptional quality bond and structural strength with the iridium center electrode DENSO patented 360 degree laser welding process: ensuring exceptional quality bond and structural strength with the iridium center electrode