Looking at an old AC Spark Plug box the ones that hold a set of 8 plugs. Printed in several locations on the box are the words " with Coralox Insulator". The numbers 5569992 are also on the box. I know they have some signifigance but do not remember what it is. Anybody know the AC plugs when they had the Coralox Insulators and what does the 5569992 number mean? Thanks Frank