Spark Plug Code: RJ12C Plug Type: RJ12C. Seat Type: Gasket. Hex Size (Inch): 0.813. Hex Size (MM): 20.65. Thread Size (Inch): 0.551. Thread Size (MM): 14. Thread Reach (Inch): 0.375. Taper Diameter (Inch): 0.28. Installed Height: 2.41. Gap (Inch): 0.027-0.033. Gap (MM): 0.69-0.84. Center Electrode Diameter (Inch): 0.1. Center Electrode Material: Nickel Copper Alloy. Ground Electrode Material: Nickel Copper Alloy. Classification: Champion Copper Plus. Resistor Plug: Y. Copper Plus spark plug has a copper core center electrode that allows for accurate control of heat range optimizing performance and longevity of the spark plug. Patented SAC-9 semi-conductor resistor for maximum and suppression. Patented Ultraseal coated shell for rust prevention.