Originally Posted by Peregrine
I would center the center electrode at the desired mark by wiggling the tool in between the ground electrode and center electrode. This should create a groove in the tool if the spacing was tight to begin with.
DO NOT WIGGLE THE TOOL IN BETWEEN THE PLUG! You will have a good chance of ruining the plug, theirs a hole on the gapper and what you want to do is to use that to gao it bigger. Especially with iridium plugs you can rub of the coating and basiacally be back to a platinum coating (some of the companies put on a coating rather than full iridium)