"V" &"X"& "Z" usually mean special gap. "K" is special design. The AC Delco book does not give a decription on what it means. I would not want to take a chance with a $1.49 plug to damage to my engine. If it's a lower resistance plug it could blow out the coil or module. If made from a special material it could self destruct under boost and damage the cyl and piston. Who knowsb4black:
I would bet the K refers to a special gap. Re-gap them and they would be fine.