NGK XR4 stock number 5858. 14mm thread size, 13/16" hex, 3/8" reach, gasket seat, resistor, projected tip, 4 heat range. NGK V-Power spark plugs feature corrosion-resistant plating and copper core for improved conductivity and heat dissipation. NGK V-Power spark plugs feature a V-cut center electrode to provide improved ignitability.