My original thread is located here: http://mustangforums.com/forum/4-6l...d-plug-in-cylinder-8-other-plug-problems.html Originally I thought my spark plug was rounded out in a Mustang I recently acquired (01 GT Convertible). After some tinkering, I found that the plug wasn't rounded out at all. It in fact is completely in tact, but wiggles a good bit in the head. It wiggles enough to indicate, to me, that the plug is just barely loose, but not enough to really move anywhere with pressure it seems. My 5/8ths socket just spins freely. I want to pick up the next size down tomorrow, although I don't know what that would be, but first I want to see if anyone else has heard of this, if this idea is even plausible, and if anyone else has any thoughts on the matter that I should know before moving forward. The #8 plug: http://i1298.photobucket.com/albums...94580E1-4826-00000116E7A7671E_zps6ae0b551.jpg The #4 plug: http://s1298.beta.photobucket.com/u...E0-4826-00000116D9FB432E_zps84f151e7.jpg.html That may also be why the cylinder misfires part of the time.