GM recommends checking and if necessary replacing your spark plugs every 35,000 miles. In 2002 a new spark plug was released for use in the 1997-2004 C5 and Z06 Corvette. The new spark plug has an Iridium tip instead of the current Platinum tip. Due to the different tip design, the gap of the spark plug has also changed. The new spark plug, ACDelco Part Number 41-985 (12571164), is gapped to 1.01mm (0.040 inches) when the spark plug is made. The spark plug gap is set during manufacturing and should not be changed to the gap required with the Platinum plug, or damage to the spark plug may result. It is also recommended to check and replace spark plug wires at spark plug maintenance interval.