I been told in here 18mm i tried a craftsman and it wouldnt fit also maddog said he thought it was 17mm I was only able to get it with a sparkplug socket tool that came with a honda recon. Maybe someone can help further solve the question cause i rather use a socket than the anoying adaptation i have to make useing the tool with crowfeet wrench to small extentsion to torqe ratchet is annoying but i like the old rusted tool it hold the plug to be able to pull it out. If you cant afford to wait are order the tool than I hope someone can tell us what size deepwell and what brand they are useing. If i remember correctly the 18 fit the plug out of box snugly I been doing so much to raptor and parts buying i forgot but down in the hole it would not fit over the plug.
I also use ngk r plug from autopart store nothing special standered plug for 3/4bucks.
Heres a question for anyone who used differnt plugs. Whats best? how much better is a ngk irrduiem over reguler ngk r?