How do you use a spark plug application chart?

Look up the device for which you are trying to replace the spark plug, and then go to the row that has the spark plug size you are trying to replace. That row contains the model numbers for the most popular brands that carry that size.

Spark plug application charts come in two varieties: those printed by car manufacturers, which include all brands of spark plugs, and those printed by spark plug manufacturers, which are often less comprehensive. If you are unable to find the spark plug you need in a plug manufacturer book, try one from one of the large car manufacturers.