Champion Copper Spark Plug - 251 Part #: 251 Line: CHP Champion Copper Spark Plug Manufacturer's Defect Warranty Seat: Tapered Thread Size: M14 Heat Range: 17 Hex Size (in): 5/8 Inch Preset Gap (in): 0.033 To 0.038 Inch Preset Gap (mm): 0.84mm To 0.97mm Thread Reach (in): 0.441 Inch Resistor Plug: Yes Center Electrode Core Material: Copper Center Electrode Tip Material: Nickel Insulator Height (in): 0.125 Inch Ground Electrode Tip Material: Nickel Metallurgy: Copper Show More Show Less