there should be a line on the middle of the tip
if the tip became round...its time to change
btw...what is the tool openner size to open the plug inside?
i got the screw driver to open the cover only...dunno the size for inside
errr... it comes with the tool set called "automotive tools set" - 60 pieces, i bought it a kuantan giant.. RM32.90
the tool size written there for spark plug is 5/8'' .. but i never try b4..