Correct size for ZX6R spark plug removal tool?

Hey guys, I have an NGK CR9E sparkplug I want to remove, it is way down in the thingo where it lives... I am trying to remove it with a 16MM spark plug remover (5/8), it "feels" like it is turning around inside the remover, I have no way to measure the size of the actual outside of the sparkplug and I dont have the spark plug remover that came with the bike, anyone got a sparkplug they can measure to see if 16MM is right?

Never mind, my socket wrench was f*cked... it is 16MM.

16 mm yes, you may need a thinwall socket if a stock one doesn't crack it.