Local color. local color-The true color of an object or a surface as seen in typical daylight, rather than its color as seen through atmosphere or interpreted by the taste or imagination of the artist. Thus the characteristic local color of a lemon is yellow.
A spark plugs reach is calculated by the length of the threads. It is measured from the seat of the plug to the end of the threads. It should be noted that the reach does not include the electrodes, or an extended metal shell. When custom-selecting a spark plug, the electrode length and projection should be included in the calculation when taking into consideration the clearance in the combustion chamber.
Simply speaking, a spark plug is just a spark gap affixed to a threaded insulated penetrator to get it into the cylinder head. The gap is from the tip of the center electrode of the plug that goes through a hermetic ceramic insulator core. Then a second terminal of the gap is made by a loop of steel connected to the outer steel ring of the plug.