When you look at standard old fashioned Nickel Spark Plugs they feature flat, rather large electrode surfaces which block the ability of the spark ignition to grow. But DENSO Iridium TT spark plugs feature two needle-thin electrodes (with the centre electrode 0.2mm smaller than the nearest rival) which act as thinner ‘fingers’, allowing the spark combustion to expand 360 degrees in all 3 dimensions.
Denso Nickel TT
Nickel TT spark plugs incorporate a similar electrode tip design, however no precious materials are used unlike Iridium TT, making the cost to efficiency ratio very good.