Just a note that for most plug manufacturers, and I’m sure for all NGK, if it has an “R” in the part list it has an internal resistor.
I use both 18mm and 14mm plugs and to be honest I’ve not really found much difference provided the ign is in good condition, plugs are clean and something around the right heat rating is used. A slight preference for 14mm just because they are easier to obtain locally.
Cheers,
Rich
