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Autolite's numbering system does not have a standardized heat range identifier.
The last digit in an Autolite part number represents the heat range within a plug family.
For example, take the 254x plug series. Autolite has 2544, 2545 and 2546 available. 2544 is the coldest plug in that plug family, and 2546 is the hotest.
However, according to an Autolite reference chart, Autolite 86 has the same heat range as 2244 and Autolite 303 is a hotter plug than 2974.
Therefore, it is impossible to chart an Autolite heat range hierarchy, let alone a standardized comparison to other spark plug brands.
E3 does not have a standardized heat range identifier.