I'm picking up an 06 350 regular cab SD next weekend. Its my first Ford since my 97 F150 Off Road that I sold in 2001. I'm concerned about the spark plugs because I'm not sure if they are original, or if they were changed. I just have a few questions if that's OK. Why is the 9/16 socket special, who makes them and where can it be purchased? Also, do you have any other tips on plug removal? Do you think that injector cleaner helped a lot? I guess the idea behind the cleaner is to remove any carbon on the plugs. Thanks