1971-1973 Arctic Cat Snowmobiles Factory Service Manual, Page 111Get this manual
ELECTRICAL General Spark Plug Information
All spark plugs basically consist of two (2) distinct electrodes separated by an air gapCompletely insulated in the core of the spark plug is the "center electrode"The "side electrode" is connected to the outer shell of the spark plug baseWhen high voltage is produced in the ignition coil, it is transferred to the center electrode, causing spark to jump the "air gap" to the side electrodeAt this time the spark which occurs inside the cylinder starts the actual combustion process
Center Electrode