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How is a Spark Plugs Reach Calculated?

Reach Location on a Spark Plug

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 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.

Please use our vehicle lookup to find the correct OE type plug for your vehicle.  Only expert engine builders should use the reverse engineer tool, or attempt to play with a plugs dimensions.


Use of an improper plug in an engine will result in engine damage.  


Reach Calculation on flat seatReach calculation on tapered seat


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