E3 Spark Plug - Cast Iron Chevy Head/Some Ford - Non-Resistor Type, for 12.5 - 14.0 compression ratio. 14mm Thread, .46" Reach, Taper Seat, Std. Tip Reach. E3's patented Edge-to-Edge design improves upon the phenomena that caused racers to cut ordinary electrode spark plugs in order to increase the number of sharp edges and improve the spark discharge. The E3 DiamondFIRE design is open at the end, so the spark travels directly toward the air-fuel mixture which maximizes the burn. The result is a faster flame kernel, a more complete combustion, greater power and higher fuel efficiency.