Spark plugs, don't you usually hand tighten and the do a 1/4 turn? That's how I have always done it. A lot of large TQ wrenches don't work well that low. Usually they start at 20lbs. I just looked on AutoZones site. They have 3 listed. 1/2 drive starts at 30ft/lbs, and a 3/8's starting at 20ft-lbs. So if you got either of these you most likely over torqued it because the tool was not rated to be able to tq that low.
2001 ZX3 2.0L Zetec-
Hatch Nation #42
Going through Rebuild See "The TICK Build Thread" for details (http://www.focusfanatics.com/forum/showthread.php?t=289168&referrerid=62897)