ACR-43 Spark Plugs

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

[SS427]

I have a box with the same 5569992 and they are not marked on the box with Coralox Insulator. My AC Delco parts book is not handly at the moment but I believe that 5569992 is just their part number. You can read an old AC ad that explains with this marketing word means with regards to the insulator.
http://www.amazon.com/Coralox-Insulator-General-Motors-Michigan/dp/B007V7SHAK

Thank you for the Coralox link

[Mr70]

Dated mid 1950's.