I hate to be the bearer of bad news but getting the remainder of the plug out may only be the small part of your problem. You, more than likely, will need to get the debris out of the cylinder. It could damage the top of the piston and/or the valves.

For sure you could get the broken plug out by removing the head and taking it to a machine shop and unless you can get a 1/2" drive socket on it I think that will end up being the way you resolve the problem. Sorry to sound bad about it but that is the way this diyer sees it. Maybe some techs have been here before and have a better answer.

For what it is worth, always use a little never seize on the spark plug threads and use a torque wrench to torque them to the specified setting.

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Jim