I'm trying to replace the spark plugs of my 2006 Prius, but the deep well 5/8 socket attached to a 2 in extender just turns loose, as if it does not fit in the top of the spark plug. I tried also 3/4 and 13/16 but those don't even fit in the spark plug well. I tried in another spark plug to the same result. What could I do to remove the spark plug?

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    Do you have a new, replacement plug? Does the socket fit on it? – JPhi1618 Dec 31 '15 at 20:22
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    The correct size is a 5/8 socket. Are you sure the little rubber grommet inside of it (to hold the plug for removal) is not in the way? It can stop you from being able to get a good grip on the plug body. – race fever Dec 31 '15 at 20:38
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    I can confirm that @racefever is correct ... it's a 5/8" deepwell (or spark plug) socket to remove the plug. Also, even on a deep well, I wouldn't think 2" worth of extension is going to be enough to get the job done ... – Pᴀᴜʟsᴛᴇʀ2 Dec 31 '15 at 20:41
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    @Paulster2 Is right, you need a 6 inch extension minimum. OP: check the link: youtube.com/watch?v=NojMqehlJLY – race fever Dec 31 '15 at 20:44
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    @gabrieldiego You do need the 5/8 spark plug socket. The inside of the socket allows the spark plug body to fit. Otherwise the socket innards just hit the spark plug body. Its a typical mistake! (: – race fever Dec 31 '15 at 21:15

A dedicated spark plug socket is the way to go here.

Regular deep well sockets don't work because the spark plug electrode will interfere with the square drive end. This is also why an extension will not help; there is nowhere for the electrode to be accommodated.

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