Spark Plug Code: RDJ8J 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 EMI and RFI suppression. Patented Ultraseal coated shell for rust prevention. Plug Type: RDJ8J. Seat Type: Tapered. Hex Size (Inch): 0.625. Hex Size (MM): 15.88. Thread Size (Inch): 0.551. Thread Size (MM): 14. Thread Reach (Inch): 0.307. Taper Diameter (Inch): 0.22. Installed Height: 1.45. Gap (Inch): 0.022-0.028. Gap (MM): 0.56-0.71. Center Electrode Diameter (Inch): 0.094. Center Electrode Material: Nickel Copper Alloy. Ground Electrode Material: Nickel Copper Alloy. Classification: Champion Copper Plus Small Engine. Resistor Plug: Y