NGK (4004) BMR4A SOLID Standard Spark Plug, Pack of 1 Designed to operate over a much wider heat range than ordinary plugs Resists carbon buildup and pre-ignition High alumina ceramics for better heat transfer and electrical insulation Solid copper core and nickel tipped electrode provide a longer plus life Patented triple gasket sealing process eliminates the possibility of combustion gas leakage Solid terminal nut Solid Terminal Nut Insulators constructed from 99 percent pure alumina silicate Solid core offers superior heat dissipation and conductivity Corrugated ribs prevent flash over