there are different type of sprak plug like platinum/iridium/copper/nickel tipped but whats the reason behind the different size of plug if the spark plug is just to burn fuel
bump..
It depends on compression chamber dimension & design and as well as amount of heat generation.
Correct word is Combustion chamber not compression chamber.
different engines have different designs, e.g. you wont want a huge plug like a 3/4 inch plug in a cd70 head would you?